A solenoid valve (30, 60) control device provided with: a rectifier circuit which is connected to an alternating-current power source and is configured to rectify an alternating-current voltage input from the alternating-current power source and output a generated full-wave rectified voltage (Vcm) through a pair of output terminals (11a, 11b); a switching element connected in series to a drive circuit of a solenoid valve (30, 60) between the output terminals of the rectifier circuit, wherein the switching element is a contact (20a, 50a) of a relay (20, 50); a current detecting circuit configured to output a first voltage when a current equal to or greater than a predetermined level is flowing in the switching element and output a second voltage different from the first voltage when the current equal to or greater than the predetermined level does not flow in the switching element, wherein the current detecting circuit comprises a photocoupler (31, 61) which includes a light-emitting diode (31a, 61a) connected in parallel to the drive circuit of the solenoid valve (30, 60) and a light-receiving transistor (31b, 61b), and wherein, when the contact (20a, 50a) of the relais (20, 50) is switched on, the light-receiving transistor is switched on when the output voltage (Vcm) from the rectifier circuit is not lower than a threshold voltage and the light-receiving transistor is switched off when the output voltage (Vcm) is lower than the threshold voltage; and a controller configured to detect whether the switching element is on state or off state according to the output voltage from the current detecting circuit, characterized in that the solenoid valve control device is further provided with a smoothing circuit (40, 70) configured to smooth and output the output voltage from the current detecting circuit; and the controller detects that the switching element is on state when the output voltage (Vb1, Vb2) from the smoothing circuit (40, 70) levels between the first voltage and a first threshold value defined between the first voltage and the second voltage a rectifier circuit which is connected to an alternating-current power source and is configured to rectify an alternating-current voltage input from the alternating-current power source and output a generated full-wave rectified voltage (Vcm) through a pair of output terminals (11a, 11b); a switching element connected in series to a drive circuit of a solenoid valve (30, 60) between the output terminals of the rectifier circuit, wherein the switching element is a contact (20a, 50a) of a relay (20, 50); a current detecting circuit configured to output a first voltage when a current equal to or greater than a predetermined level is flowing in the switching element and output a second voltage different from the first voltage when the current equal to or greater than the predetermined level does not flow in the switching element, wherein the current detecting circuit comprises a photocoupler (31, 61) which includes a light-emitting diode (31a, 61a) connected in parallel to the drive circuit of the solenoid valve (30, 60) and a light-receiving transistor (31b, 61b), and wherein, when the contact (20a, 50a) of the relais (20, 50) is switched on, the light-receiving transistor is switched on when the output voltage (Vcm) from the rectifier circuit is not lower than a threshold voltage and the light-receiving transistor is switched off when the output voltage (Vcm) is lower than the threshold voltage; and a controller configured to detect whether the switching element is on state or off state according to the output voltage from the current detecting circuit, characterized in that the solenoid valve control device is further provided with a smoothing circuit (40, 70) configured to smooth and output the output voltage from the current detecting circuit; and the controller detects that the switching element is on state when the output voltage (Vb1, Vb2) from the smoothing circuit (40, 70) levels between the first voltage and a first threshold value defined between the first voltage and the second voltage