The invention provides an organism authentication device. In the organism authentication device, a task exists in educing for realizing an appropriate organism placement mode. Additionally, a task exists in alarming when a placement mode which stops blood flow occurs. At a position for placing the organism, a sensor (contact sensor) for detecting whether the organism is placed is arranged, and furthermore whether the current placement mode is an appropriate organism placement mode is detected. As a detecting result, on condition that the determining result is the appropriate organism placement mode, organism registration or authentication is performed.