In a piezoelectric oscillator a non-inverted output terminal (3) of an ECL circuit (10) is grounded via a capacitor (C3) and is connected to a non-inverting input terminal (5) of the ECL circuit (10) via a series connection of capacitors (C4) and (C5). The non-inverting input (5) is connected via a resistor R1 to an inverting input terminal (4) of the ECL circuit (10) and is grounded via a capacitor (C2). The connection point of the series connection of the capacitors (C4) and (C5) is grounded via a crystal oscillator (X'tal) and a frequency control capacitor (C1). The output from the ECL circuit (10) is provided at its inverted output terminal 2.