TWI770309B

To inspect the presence or absence of air bubbles in a liquid flowing in a conduit.SOLUTION: Provided is an inspection device which is disposed in a conduit being a flow path of a liquid, includes: two ultrasonic transducers disposed upstream and downstream of the conduit; and a control unit electrically connected to the two ultrasonic transducers. The control unit includes an amplitude calculation unit, a determination unit, and an amplitude range registration unit. The amplitude calculation unit calculates an amplitude of a first ultrasonic wave generated in one of the two ultrasonic transducers and propagating in the liquid flowing in the conduit, from waveform information obtained by observing the first ultrasonic wave using the other of the two ultrasonic transducers. In the amplitude range registration unit, the range of the amplitude of ultrasonic waves propagating in the liquid in which air bubbles are mixed is registered. The determination unit determines that air bubbles are mixed in the liquid when