PURPOSE: To prevent incorrect control at the connection of power supply, by providing the titled device with a circuit to inhibit developer feeding or alarm operation of an alarming means during a prescribed period after power supply.

CONSTITUTION: When a bubble is detected in circuit operation, only an AC component out of signal voltage V1 outputted from a photodetector 9 is inputted to an integrating circuit through an impedance converting circuit consisting of a transistor (TR) Q22. When the integration value is higher than the prescribed voltage, i.e. the input voltage V2 of an operational amplifier Q23 is reduced lower than the voltage set by a variable resistor VR4, a TRQ26 is actuated. Consequently the reduction of liquid quantity is displayed by a lamp PL1 through the TRQ26 and the base potential of a TRQ28 is turned to "0", so that the operation of a solenoid SL is stopped. Since the AC component is detected, malfunction due to two or three bubbles or the unevenness of density is removed. Thus incorrect control at the time of power supply can be prevented.