To provide an third-order function generating circuit which can be realized in a CMOS process and makes the precise compensation of temperature possible, and to provide a crystal oscillator in which the third-order function generating circuit is mounted.

There are provided a logarithmic voltage conversion circuit 7, in which a current It which varies with the temperature and a constant current IO which is independent of the temperature are inputted and the currents are converted into voltages by bipolar transistors Q1 and Q2, respectively, a triple amplifier 8, in which the voltages converted by the logarithm voltage conversion circuit 7 are inputted and the voltage converted by the bipolar transistor Q1 is tripled by the voltage, converted by the bipolar transistor Q2 as the reference; and an exponent current conversion circuit 9, in which the output voltage of the triple amplifier 8 is inputted to a base terminal and the voltages are converted into currents by a bipolar transistor Q3 or the like. Then, these circuits are provided in the temperature compensated circuit of the crystal oscillator.