When a ring with an exposed dental X-ray film mounted thereon is thrown into a first tank filled with a processing solution, the ring is scooped into a space of a ring-holding portion of a rotating arm through a first opening. As the ring-holding portion is moving in the tank, the ring is pushed by a tilted bottom portion while being held within the space by a release preventing wall and a door so that the ring is also moving together with the ring-holding portion. When the ring-holding portion has fully moved out of the tank, the door is opened and the ring is released from the space into an adjacent tank through a second opening.