A flow passage device includes a circulation flow passage, a swing valve provided in the circulation flow passage, an energizing part, and a lock mechanism including a lock pin. The lock pin is configured so as to hinder the swing valve from opening, and to allow the swing valve to open. The swing valve is configured so as to rotate from a first valve position to a second valve position. The lock mechanism is configured so as to set a locked state and to set an unlocked state. The lock pin is configured so as to protrude as being energized by pressure of the fluid on an upstream side of the swing valve, and to retract as being energized by pressure of the fluid on a downstream side of the swing valve.