A current mode synchronous rectification direct current (DC)/DC converter according to the present invention includes: a soft start function unit (in FIG. 1, a reference voltage generation unit (104) enabling a reference voltage REF to slowly increase while starting), for inhibiting a target value of an output voltage VO to be lower than that at a normal action while starting; and an output stabilization function unit (in FIG. 1, a frequency variable type oscillator (110A) generating a clock signal CLK and a slope voltage SLOPE through an oscillation frequency corresponding to a reference voltage REF), for performing at least one of waiting for start of a switching action and reduction of a drive frequency while starting.