An image pickup apparatus includes a lens, and a solid-state image sensor for converting light which passes through the lens into an electric signal. A signal processing circuit serves to process the electric signal outputted from the solid-state image sensor. A Gray code counter serves to count pulses of a first clock signal and to generate Gray codes in response to the first clock signal. A device functions to feed a second clock signal and a synchronizing signal to the solid-state image sensor and the signal processing circuit in response to the Gray codes generated by the Gray code counter respectively. A counter circuit includes n-bit counting stages where n denotes a predetermined natural number, and a plurality of logic decoders for feeding logic outputs to input terminals of the respective counting stages, the logic outputs being equivalent to a product of a first logic output of a (k-1)-th-bit counting stage and second logic outputs of a (k-2)-th-bit counting stage and lower-bit counting stages where k denotes a natural number between 3 and n.