Abstract: An integrator is disclosed that is capable of outputting the same integration result with respect to the same bit pattern even if there are fluctuations in the integrating period, semiconductor device process, or the power supply voltage. The disclosed integrator includes: (1) a first integrator having a first amplifier, for integrating a reference voltage during an integrating period, (2) a second integrator having a second amplifier, for integrating an input signal during the integrating period, and (3) control means for outputting a signal regulating a gain of the first amplifier to the first amplifier so that an output of the first integrator varies in correspondence with the integrating period, and for regulating a gain of the second amplifier by means of the signal.