A secondary vibration damping type crystal oscillator circuit is formed as a Colpitts type, in which a crystal unit is connected between base and collector terminals, a first capacitor is connected between emitter and collector terminals, and a second capacitor is connected between emitter and base terminals of a oscillating transistor. A region between the emitter and collector terminals or between the emitter and base terminals includes a reactance parallel circuit, in which an LC series circuit is connected in parallel to the first or second capacitor. The reactance parallel circuit has resonant characteristics that the reactance parallel circuit is made capacitive at an oscillating frequency in principal vibration mode of the crystal unit as an oscillating frequency, and a resonant frequency of the LC series circuit corresponds to the vibrational frequency in secondary vibration mode that is close to the principal vibration mode.