An oven controlled crystal oscillator includes a crystal unit, a temperature control circuit, and a circuit board. The temperature control circuit is configured to control a temperature of the crystal unit. The crystal unit includes a flange that projects outward to an entire outer periphery in one end. The circuit board includes a depressed portion in which the flange is partially inserted. The temperature control circuit includes a power transistor, a thermistor as a temperature sensor, and a metal pattern. The power transistor becomes a heat source. The metal pattern commonly connects a ground terminal of the crystal unit, a collector of the power transistor, and a ground terminal of the thermistor. The crystal unit is positioned in a state where the flange is partially inserted in the depressed portion. The crystal unit is connected to the metal pattern.