In an inverter oscillation circuit an output terminal 2 of an inverter 1 with its input and output interconnected via a high resistance R1 is grounded via a series connection of a capacitor C1 and parallel tuning circuit composed of a capacitor C2 and an inductor L1 connected in parallel, and the connection point of this series connection is grounded via a parallel circuit of diodes D1 and D2 connected in opposite polarities. The connection point of the series connection is connected to an input terminal 3 of the inverter 1 via series-connected capacitors C3 and C4, and the connection point of this series connection is grounded via a piezoelectric vibrator Xtal and a frequency adjusting capacitor C7. The inverter oscillation circuit is configured to provide its output via a series circuit composed of a resistor R2 and a capacitor C6.