Japanese slot machines, known as pachisuro or pachislo (portmanteaus of the words "pachinko" and "slot machine"), are a descendant of the traditional Japanese pachinko game. Slot machines are a fairly new phenomenon and they can be found in mostly in pachinko parlors and the adult sections of amusement arcades, known as game centers.

The machines are regulated with integrated circuits, and have six different levels changing the odds of a 777. The levels provide a rough outcome of between 90% to an astonishing 160% (200% if using skills). Indeed, most of the machines to collect money, but intentionally place a few paying machines on the floor so that there will be at least someone winning, encouraging players on the losing machines to keep gambling, using the psychology of the gambler's fallacy.

Despite the many varieties of the machines, there are certain rules and regulations put forward by the "Security Electronics and Communication Technology Association", an affiliate of the National Police Agency. For example, there must be three reels. Also, all reels must be accompanied by buttons which stop these reels, the reels may not spin faster than 80 revolutions per minute, and the reels must stop within 0.19 seconds of the button press. In practice, this translates to "the machines can't let the reels slip more than 4 symbols". Other rules include the following: no more than 15 coins can be paid out per play, credit meter can't go higher than 50, 3 coin maximum bet, etc.

Although a 15 coin payout may seem ridiculously low, the regulations allow "Big Bonus" (~400–711 coins) and "Regular Bonus" modes (~110 coins) where these 15 coin payouts occur nearly continuously until the bonus mode is finished. While the machine is in bonus mode, the player is entertained with special winning scenes on the LCD display, and energizing music is heard, payout after payout.

Three other unique features of Pachisuro machines are "Stock", "Renchan", and tenjō (天井^?). On many machines, when enough money to afford a bonus is taken in, the bonus is not immediately awarded. Typically the game merely stops making the reels slip off the bonus symbols for a few games. If the player fails to hit the bonus during these "standby games", it is added to the "Stock" for later collection. Many current games, after finishing a bonus round, set the probability to release additional stock (gained from earlier players failing to get a bonus last time the machine stopped making the reels slip for a bit) very high for the first few games. As a result, a lucky player may get to play several bonus rounds in a row (a "Renchan"), making payouts of 5,000 or even 10,000 coins possible. The lure of "Stock" waiting in the machine, and the possibility of "Renchan" tease the gambler to keep feeding the machine. To tease him further, there is a tenjō (ceiling), a maximum limit on the number of games between "Stock" release. For example, if the tenjō is 1,500, and the number of games played since the last bonus is 1,490, the player is guaranteed to release a bonus within just 10 games.

Because of the "Stock", "Renchan", and tenjō systems, it is possible to make money by simply playing machines on which someone has just lost a huge amount of money. This is called being a "hyena". They are easy to recognize, roaming the aisles for a "Kamo" ( "sucker" in English) to leave his machine.

In short, the regulations allowing "Stock", "Renchan", and tenjō transformed the Pachisuro from a low-stakes form of entertainment just a few years back to hardcore gambling. Many people may be gambling more than they can afford, and the big payouts also lure unsavory "hyena" types into the gambling halls.

To address these social issues, a new regulation (Version 5.0) was adopted in 2025 which caps the maximum amount of "stock" a machine can hold to around 2,000–3,000 coins' worth of bonus games. Moreover, all Pachisuro machines must be re-evaluated for regulation compliance every three years. Version 4.0 came out in 2025, so that means all those machines with the up to 10,000 coin payouts will be removed from service by 2025. Only time will tell how these changes will affect the Japanese Pachisuro industry.