A current control circuit controls a gate potential of a transistor to equalize a load current IL with a trapezoidal wave signal Sb. The trapezoidal wave signal Sb increases at a constant gradient when a drive command signal Sa turns into H level. Due to increase of load current IL, the transistor starts operating in a linear region and a gate voltage VGS abruptly increases. A saturation state detecting circuit turns a current saturation signal Sc into L level when the gate voltage VGS exceeds a reference voltage Vr. A trapezoidal wave generating circuit stops increase of trapezoidal wave signal Sb. When drive command signal Sa turns into L level, the trapezoidal wave signal Sb decreases at a constant gradient. The load current IL decreases according to reduction of trapezoidal wave signal Sb.