The present invention relates to an oven controlled crystal oscillator that can obtain stable oscillation frequency by reducing a temperature change in an oscillation element. The oven controlled crystal oscillator comprises; a heat-conducting plate mounted on one surface of a circuit board, a crystal resonator mounted on a surface of the heat-conducting plate opposite to the surface of the circuit board, an oscillation element constituting an oscillation circuit together with the crystal resonator, and a thermistor that detects temperature of the crystal resonator, a heating resistance which heats the crystal resonator, and a temperature control element including at least a power transistor, to constitute a temperature control circuit together with the thermistor and the heating resistance. In the oven controlled crystal oscillator, two or more open areas communicating with the heat-conducting plate at least in the thickness direction thereof are formed on the periphery of the heat-conducting plate at positions point-symmetric with respect to the crystal resonator, and one or more of each of the power transistor and the heating resistance are arranged in the same number in all of the open areas.