Urine amount estimation device 100 is provided with ultrasonic sensor 1 which transmits ultrasonic waves into the body and which detects waves produced by reflection of ultrasonic waves； and estimating unit 52 which estimates the amount of urine in the bladder based on whether reflected wave W3 from the bladder detected by ultrasonic sensor 1 is present and/or based on the magnitude of reflected wave W3 from the bladder detected by ultrasonic sensor 1.
