A switching power source device IS capable of guaranteeing a normal switching operation even when the input of a coil voltage used for adjusting a dead time is eliminated. The cam assembly also includes a torsional spring having a pair of stationary outer arms and a pair of pivotable inner arms, wherein the pair of stationary inner arms is coupled to a portion of the first cam arm. A first direction and a second direction are defined to be orthogonal. The chip area needed for the circuit is strongly reduced by such an arrangement. After the judgment of excess, the controller judges whether detecting point corresponding to the voltage level of 3.