A shared image generation apparatus generates a basis matrix on the basis of a graph, the vertex set of which corresponds to a set of a plurality of members to which shared images are to be distributed, and generates a plurality of shared images to be distributed to the plurality of members on the basis of the basis matrix and an externally input secret image to be shared. Sensors are provided for measuring the sound generated by a test fluid when it flows through the filter element. The control circuit controls the pulse width modulator to provide pulses to the plurality of phases to control a speed of the BLDC motor by causing the pulse width modulator to adjust widths of the pulses when a measured current in an active one of a corresponding phase exceeds a threshold in a startup mode.