A detergent reservoir reserves detergent for cleaning of a sample probe and includes a cleaning liquid supply port, a detergent supply port, and a waste liquid port When a predetermined condition for execution of cleaning of the detergent reservoir is not satisfied, and a remaining amount of the detergent reserved in the detergent reservoir is a predetermined amount or less, a pump is operated to increase the remaining amount of the detergent to the predetermined amount; and when the predetermined condition for execution of cleaning of the detergent reservoir is satisfied, a solenoid valve is opened to dispose of the detergent in the detergent reservoir. Then, after the detergent in the detergent reservoir is disposed of, the solenoid valve is closed, and a pump is operated to supply cleaning liquid to the detergent reservoir.