PURPOSE: To make it possible to stably control the output of an electro-magnetic pump, by utilizing a pulse current having a constant peak value and a constant period, and by changing the duty ratio of the pulse current.

CONSTITUTION: The terminal voltage, as a negative feed-back, of the emitter side of a transistor Q2 to which a resistor R9 is connected, is applied to the inversion input of a differential amplifier A through a resistor R10, and therefore, the crest value of a current applied to a transistor Q2 is always maintained at a constant value. Accordingly, a pulse current having a constant period (t) and a constant crest and as well having a duty ratio which is determined by the value of a variable resistor RV, is applied to a winding L, thereby the output of the electromagnetic pump may be stably controlled in accordance with the duty ratio.