A
switching power source device includes current control pulse generating means configured of a target value setting module, which outputs a changeable value which is a predetermined target value relating to a control of an output current, a computing module, which carries out a computing process relating to the control of the output current based on the target value, and outputs a computation result, and a pulse generating module, which generates a current control
pulse voltage for controlling the output current based on the computation result. The
switching power source device includes a current detecting circuit, which detects the output current or a current flowing in a switching element TR1, and a current limit
signal generating circuit which, when the detected current exceeds a reference
value set based on the output of the current control pulse generating means, outputs a current limit
signal for limiting the current. A drive pulse generating circuit, on the current limit
signal being output, operates in such a way that an on-duty of a drive pulse stops widening, or becomes narrower.