A constant-temperature type crystal oscillator includes: a crystal unit that is installed on one principal surface of a circuit substrate, and chip resistors, which function as heating elements, and which are installed on the other principal surface of the circuit substrate so as to face a principal surface of the crystal unit, the chip resistors heating up the crystal unit to keep an operational temperature of the crystal unit constant. A heating metal film facing the principal surface of the crystal unit is provided on the one principal surface of the circuit substrate. A heat conducting material is interposed between the principal surface of the crystal unit and the heating metal film to perform thermal coupling therebetween. The heating metal film is thermally coupled to electrode terminals of the chip resistors via a plurality of electrode through holes.