PURPOSE: To realize a switching-type constant current driving method which is suited to the constant current driving via the large current featuring an extremely short rise and fall time each.

CONSTITUTION: Both main control transistor part 3 and semiconductor switch 6 are turned off at time point t1 when current I reaches upper limit set value IH. Accordingly, the energy so far stored in inductance element 4 flows via the closed circuit of load 5, current detector 7, free wheeling diode 8 and element 4 each. Current I of this period is decreased in the slope determined by inductance L of element 4 and resistance value R of load 5. And when current I reaches lower limit set value IL, 1st operation circuit 11 operates again to give the ignition to SCR13 and thus to turn off part 3. Accordingly, after time t2, current I increases again in the slope determined by inductance L and resistance R. After this, the current changes within the range between values IH and IL.