PURPOSE: To obtain an integration circuit with an excellent temperature characteristic through a simple configuration for a multi-purpose filter.

CONSTITUTION: Transistors(TRs) Q3, Q4 being diode loads are connected to a 1st differential amplifier circuit comprising TRs Q1, Q2 whose common emitter connects to a 1st constant current source, and a voltage subjected to logarithmic transformation obtained between emitters of the TRs Q3, Q4 is fed to a 2nd differential amplifier circuit comprising TRs Q5, Q6 whose common emitter connects to a 2nd constant current source. Then an output of the 2nd differential amplifier circuit is fed to a capacitor 36 via a current mirror circuit comprising a diode 37 and a Tr Q7 to control a current ratio of the 1st and 2nd constant current sources (I1/I2) thereby controlling the gain.