A capacitance detection circuit for detecting a small capacitance between a movable electrode and a fixed electrode in a physical quantity sensor , with these movable electrode and fixed electrode being adapted to generate a change in capacitance in response to a change in physical quantity, the capacitance detection circuit comprising, at least: said physical quantity sensor ; a bias voltage generating circuit that is adapted to generate a bias voltage to be supplied to one of the movable and fixed electrodes; an operational amplifier that has input terminals, with the other one of the movable and fixed electrodes being input to one of the input terminals while the other one of the terminals being connected to the ground; and a printed circuit board on which the physical quantity sensor , the bias voltage generating circuit , and the operational amplifier (Q21) are mounted, characterized in that an insulation-secured area (Ais) on the printed circuit board is configured as a moisture absorption reduction area (A1), this insulation-secured area (A1) including at least an electrode connection pad of the physical quantity sensor, an input-side connection pad of the operational amplifier, and connection pads connected to an input side of the operational amplifier, out of connection pads of input-side circuit components connected between the electrode connection pad and the input-side connection pad, and in that the moisture absorption reduction area (A1) forms a resist-applied area (A11) that is applied with a resist to cover the insulation-secured area (Ais), and a band-like separation area (A12) that surrounds the insulation-secured area (Ais) in such a manner as to separate the resist-applied area (A11) from a resist-applied area (A13) therearound, the band-like separation area (A12) being configured as a non-resist-applied area and as a non-silk-printing area. said physical quantity sensor ; a bias voltage generating circuit that is adapted to generate a bias voltage to be supplied to one of the movable and fixed electrodes; an operational amplifier that has input terminals, with the other one of the movable and fixed electrodes being input to one of the input terminals while the other one of the terminals being connected to the ground; and a printed circuit board on which the physical quantity sensor , the bias voltage generating circuit , and the operational amplifier (Q21) are mounted, characterized in that an insulation-secured area (Ais) on the printed circuit board is configured as a moisture absorption reduction area (A1), this insulation-secured area (A1) including at least an electrode connection pad of the physical quantity sensor, an input-side connection pad of the operational amplifier, and connection pads connected to an input side of the operational amplifier, out of connection pads of input-side circuit components connected between the electrode connection pad and the input-side connection pad, and in that the moisture absorption reduction area (A1) forms a resist-applied area (A11) that is applied with a resist to cover the insulation-secured area (Ais), and a band-like separation area (A12) that surrounds the insulation-secured area (Ais) in such a manner as to separate the resist-applied area (A11) from a resist-applied area (A13) therearound, the band-like separation area (A12) being configured as a non-resist-applied area and as a non-silk-printing area. <EOS>