Provided is a fundamental wave/overtone crystal oscillator to obtain fundamental wave oscillation and overtone oscillation with one crystal unit and to optimize the excitation current depending on the fundamental wave oscillation and the overtone oscillation. The fundamental wave/overtone crystal oscillator includes a crystal unit that oscillates with fundamental waves or with overtones, and an oscillator circuit that amplifies an excitation current from the crystal unit and outputs an oscillatory frequency. A capacitor Cf and a capacitor Co are connected in parallel with the base of a transistor in the oscillator circuit as well as the emitter. A switch is provided so as to connect or disconnect the capacitor Cf with respect to the circuit in response to a switching signal. The switch turns ON when the crystal oscillator oscillates with fundamental waves, and turns OFF when the crystal oscillator oscillates with overtones.