To provide a compact sinusoidal wave output type crystal oscillator with low consumption current.

A Colpitts type crystal oscillation circuit having a crystal resonator and an oscillating transistor, and a base-grounded amplifier type buffering transistor are provided. The oscillating transistor and the buffering transistor are connected in cascade via a resistor for cutting alternating current, one end of the crystal resonator is grounded through an interval between the base and the emitter of the buffering transistor, and the collector of the oscillating transistor is grounded in an alternating current way. As a direct current, since an oscillating transistor 2 and a buffering transistor 7 are connected in cascade (cascade connection), the collector currents of both the transistors can be commonly utilized, thereby enabling the compact sinusoidal wave output type crystal oscillator with low consumption current to be realized.