PURPOSE: To obtain an inexpensive solid state image pickup device without lowering a quality of an image data by lengthening a second period of a clock signal in a reading cycle relative to the first period of the clock signal, and reading an image information read by the first period by the second period.

CONSTITUTION: A clock signal CK of a predetermined frequency outputted from a clock signal generating section 1 is inputted to a clock signal changing- over section 5, herein, according to a processing cycle of an image sensor, two types of frequencies f1, f2 are produced and a clock signal KK is outputted by switching them properly. An image information, after photoelectrically converted (IA) synchronously with the clock signal KK in an image section 2, is transferred to (TA) to a storage section 3, an electric charge pattern stored in this storage section 3 once is transferred by a standard scanning system, read (RA) from a reading register 4, and an image signal PSA is outputted. Such cycle is the same as the conventional one. These cycles of a photoelectric conversion, a transferring, a storage and a reading are controlled by the clock signal KK from the clock signal changing-over section 5.