To provide a logarithmic transformation circuit which expands a dynamic range without receiving the influence of the bias current of an operational amplifier.

The logarithmic transformation circuit comprises a p-n junction type transistor Tr and the operational amplifier OP, has an input current I and the forward current Ie of the transistor Tr inputted to the input terminal of the operational amplifier OP and has the forward voltage of the transistor Tr determined by the output voltage of the operational amplifier OP. Compensation current injection circuits (OP2, R1, R2) for injecting a compensation current Ib' of nearly the same amplitude with a bias current Ib and of an inverse polarity to the input terminal independently from the operational amplifier OP to the input terminal of the operational amplifier OP.