A processing circuit (30) is provided which includes at least an integrator circuit which uses a reference voltage (Vr) set to have a predetermined magnitude as an operation reference and which integrates a detection signal (Qi) so as to convert the detection signal (Qi) into a voltage waveform and a base voltage adjustment circuit (40) which is connected between an input terminal and an output terminal of the integrator circuit and which adjusts the magnitude of a base voltage (Vb1) that is a potential when the detection signal (Qi) in an output signal (Vout1) output from the integrator circuit is not present. As another form, a processing circuit (30) can be adopted which includes at least one or more amplifier circuits which amplify an output signal (Vout21) from an integrator circuit and a base voltage adjustment circuit (40) which is connected between a supply portion of a reference voltage (Vr) fed to the amplifier circuit and an input terminal of at least one of the amplifier circuits and which adjusts the magnitude of a base voltage (Vb22) that is a potential when a detection signal (Qi) in an output signal (Vout22) output from the amplifier circuit is not present.