A constant-temperature type crystal oscillator includes: a crystal unit including a case main body including a first power source terminal on an outer bottom surface thereof; a surface-mounted oscillator; a temperature control circuit including a heating resistor and a temperature sensor; and a circuit substrate including a second power source terminal. One ends of the heating resistor and the temperature sensor are electrically connected to the second power source terminal. The first power source terminal of the surface-mounted oscillator and the one ends of the heating resistor and the temperature sensor are electrically connected to the second power source terminal of the circuit substrate. The first power source terminal of the surface-mounted oscillator is directly and electrically connected to, at least, the one end of the temperature sensor via an electrically-conducting path.