An oven-controlled crystal oscillator includes a circuit board, a crystal unit surface-mounted on the circuit board, and a temperature control circuit that maintains operating temperature of the crystal unit constant. The temperature control circuit includes a heating resistor, a power transistor that supplies power to a heating resistor, and a temperature sensitive resistor that detects temperature of the crystal unit. The heating resistor is formed, as a film resistor, on a surface of the circuit board in an area thereof in which the crystal unit is located. The temperature sensitive resistor is provided on the circuit board as a film resistor.