To configure a triangular wave oscillation circuit with a smaller number of circuit elements.

In the configuration that a charging operation and a discharging operation to a capacitor 22 are switched by the output signals of a comparator 5 and a charging/discharging circuit 3 repeats the operation of charging the capacitor 22 from the lower limit voltage to the upper limit voltage of an oscillation voltage by a fixed charging current and discharging it from the upper limit voltage to the lower limit voltage by a fixed discharging current after it is charged, an oscillation voltage setting circuit includes a diode 33 inserted in a route where a constant current flows inside a constant current circuit 32 for supplying a bias current to respective circuit parts, and a changeover switch 21 for switching the terminal voltage on the anode side and cathode side of the diode 33 and outputting it as a reference voltage for comparison of the comparator 5.