A comparator device comprising a offset-compensating comparator and a positive-feedback comparator. A reference voltage and an input voltage are applied to the input terminals of the offset-compensating comparator. The non-inverting and inverting output terminals of the offset-compensating comparator are connected to the inverting and non-inverting input terminals of the positive-feedback comparator, respectively. The positive-feedback comparator starts comparing the input voltage with the reference voltage before the offset-compensating comparator finishes comparing the input voltage with the reference voltage. Hence, the comparator device operates at high speed and has a great gain. In addition, the offset voltage can be reduced. A transistor is connected between the differential input terminals of the positive-feedback comparator, for setting both differential input terminals at the same potential at the time the comparator starts comparing the input voltage with the reference voltage. Therefore, the differential inputs to the positive-feedback comparator have no noise.