A wireless plethysmogram sensor unit is capable of obtaining a plethysmogram from a living tissue of a measuring object and of transmitting the plethysmogram to a processing unit outside the wireless plethysmogram sensor unit. The sensor unit includes a light source to emit measuring light into the living tissue and a light receiving element to receive light emerging from the tissue, which is accompanied by pulsation caused by absorption by arteries in the tissue. A memory stores a plethysmogram obtained in accordance with the light received by the light receiving element. A short range wireless communicator transmits the plethysmogram to the processing unit. A power source provides power to other elements in the sensor unit, and a controller controls the elements of the sensor unit.