PURPOSE: To reduce the variance of a circuit current for each production lot and to extend the high frequency characteristic by using polysilicon resistances as collector load resistances of differential transistors TRs on the same semiconductor substrate and using a diffusion resistance as the emitter resistance of a constant current source circuit.

CONSTITUTION: A pair of differential TRs 11 and 12 for amplifying action, a constant current source TR 10 which has the collector connected to the common emitter point of TRs 11 and 12 and to which a resistance 20 is connected in series, the diffusion resistance connected in series to the emitter of the constant current source TR 10, and polysilicon resistances connected to collectors of differential TRs 11 and 12 as load resistances 21 and 22 are formed on the same semiconductor substrate. That is, the variance for each production lot is reduced because the diffusion resistance which has a high absolute precision and a satisfactory reproducibility is used as the resistance 20. Meanwhile, excellent high frequency characteristic and switching characteristic are obtained because polysilicon resistances of small stray capacity are used as resistances 21 and 22.