Beachgoers have been advised to avoid the dolphin-infested waters as one particular creature is suspected to be behind the attacks.
The adult bottlenose is thought to have struck on beaches including Koshino and Takasu .
Most severely, one victim had 14 stitches to treat a bite on their hand.
Local news outlet Fukui Shimbun reported the attack on two men, which occurred six hours apart on Thursday.
Experts had earlier introduced ultrasonic devices underwater to deter the dolphins – although two attacks took place after its installation.
According to the Echizen Matsushima Aquarium in Fukui, the dolphin behind the chaos is thought to be an Indo-Pacific bottlenose dolphin.
Aquarium staff noted that the attacks were likely by the same dolphin, identified by descriptions, that was first seen in April.
Police have begun patrolling the shores and warning people with leaflets to watch their distance before beaches close.
Dolphin attacks are not common, but can happen on occasions where animals feel unsafe.
Speaking to the Mainichi Shimbun, Tatsumi Iwasa, 71, who owns a local café said that “"dolphins used to push people, but recently their behavior has escalated to the point where they’re lunging on top of them."