A cell detachment device includes: a base; a vessel holder, to which a culture vessel is to be fitted; a guide mechanism configured to guide reciprocating movement of the vessel holder; a collided member configured to collide with the vessel holder when the vessel holder is moving; an urging member configured to urge the culture vessel toward the collided member; and a power imparting mechanism configured to impart, to the vessel holder, power for causing the vessel holder to move.