PURPOSE: To provide the triangular wave oscillating circuit whose oscillating frequency and oscillating amplitude are stable even when a drive power supply voltage is subjected to change.

CONSTITUTION: A constant voltage source 3 is used for a constant current source by using an amplifier 4, a buffer 6 and a resistor 5, its constant current is used for a charging current and a discharge current for a capacitor 20, and a voltage across the capacitor 20 is compared with a voltage at other terminal of a resistor 26 whose one terminal connects to the constant voltage source 30 at a comparator comprising transistors (TRs) 16,17. A constant current flows in/out of the resistor 26 in interlocking with the changeover of charging/ discharging of the capacitor 20 and then the voltage at the other terminal of the resistor 26 is switched. The voltage across the capacitor 20 is changed in a triangle shape by comparing the voltage at the other terminal of the resistor 26 with the voltage across the capacitor 20 to switch the charging/ discharging of the capacitor 20 and the flowing in/out of the current to/from the resistor 29.