PURPOSE: To attain highly precise A/D conversion even in the operation of the circuit with a low voltage by providing a variable timing setting section setting a period of a 1st stage of A/D conversion longer than a period of the succeeding stage to a control circuit which provides a voltage a half the reference voltage to a conversion section at the 1st stage.

CONSTITUTION: A control circuit 12 sets a time required for changing a charge to a capacitor 6 longer in the operation under a low power supply voltage when a resistance of a 1st analog switch 3 is switched to be largest and a reference voltage being a half of a reference voltage VREF is compared with a voltage to be compared. That is, the control circuit 12 controls on/off timing of 1st-5th analog switches 4, 5, 8, 91, 92, 31, 32, 33 and uses a variable timing setting section 20 to set a time of a period in a 1st A/D conversion stage longer than that of the succeeding stage. As a result, when the A/D converter circuit is operated under a low power supply voltage, even when a conduction resistance of the analog switch 32 is highest around at a voltage of (1/2)Vcc, the capacitor 6 is sufficiently charged up and then the precision of A/D conversion is secured.