Abstract: First and second analogue signal processing circuit has first to fourth input terminals and first and second output terminals, and functions such that the first and second output terminals have an equal potential and that a difference between output currents of the first and second output terminals is proportional to a product obtained by multiplying a potential difference between the first and second input terminals by a potential difference between the third and fourth input terminals. The first input terminal of the first analogue signal processing circuit is supplied with an input signal, and the second input terminal is supplied with ground potential. The third input terminal is supplied with a second reference potential, and the fourth input terminal is supplied with a third reference potential. The first input terminal of the second analogue signal processing circuit is supplied with an output signal from an operational amplifier, and the second input terminal is supplied with the ground potential.