A compact image input apparatus is operable under low power consumption, while omitting a buffer memory for storing image data, which is originally required to transfer image data between this image input apparatus and a personal computer. The image input apparatus is arranged by an image sensor for optically sensing an image of an object to produce an analog image signal; an A/D (analog-to-digital) converter for A/D-converting the analog image signal derived from the image sensor into a digital image signal; an interface control unit for converting the digital image signal derived from the A/D converter into image data; an image sensor driving unit for driving the image sensor; an A/D converter driving unit for driving the A/D converter; a clock oscillator for oscillating a clock signal; a clock switching control unit for controlling a supply of the clock signal to the image sensor driving unit and the A/D converter driving unit in response to the clock signal produced from the clock oscillator, and both a transfer starting signal and a transfer clock signal supplied from the interface control unit; and a personal computer for receiving the image data converted by the interface control unit and for supplying the transfer starting signal to the interface control unit. The clock switching control unit includes drive means for supplying the clock signal produced form the clock oscillator to the image sensor, and also for not supplying the clock signal to the A/D converter driving unit within a preset time period after the transfer starting signal is received.