To provide an image signal readout circuit, to be used for constituting a hybrid type infrared ray image sensor, etc., wherein the usage efficiency of a signal electric charge is enhanced and the S/N ratio of an image signal can be improved.

The signal electric charges from a photodiode 21 are stored in potential wells 25, 29. The signal electric charges stored in the potential well 29 are transferred to a potential well 31, and the signal electric charges stored in the potential well 25 are discarded to an overflow drain OFD. After this, the similar operations are repeated, and the signal electric charges are transferred to the potential well 31 to be integrated. After the integration period is ended, the signal electric charges stored in the potential well 31 are transferred to an n-type region 33.