A constant current driving circuit for supplying a constant current to a load circuit includes: a first driver circuit having a pulse width converting circuit for converting a first difference detection signal into a pulse signal having a pulse width corresponding to a signal level of the first difference detection signal, a switch turned on/off on a basis of the pulse signal, and a smoothing circuit for supplying a smoothed first load current to the load circuit; a first current detecting circuit for converting the first load current into a first voltage corresponding to the first load current, and outputting a first current detection signal; a second driver circuit for supplying a second load current to the load circuit on a basis of a signal level of a second difference detection signal; a second current detecting circuit for converting the second load current into a second voltage corresponding to the second load current, and outputting a second current detection signal; a first difference detecting circuit for calculating the first difference detection signal to make zero a difference between the first current detection signal and an input voltage; a second difference detecting circuit for detecting a difference voltage between the first current detection signal and the input voltage, and outputting a third difference detection signal; and a third difference detecting circuit for detecting a difference voltage between the third difference detection signal and the second current detection signal, and outputting the second difference detection signal.