PURPOSE: To obtain a picture signal which is stable regardless of a change of the scanning speed by writing the charge store time of a sensor to a memory of one side after keeping said store time for each line to read the written store time out of the memory during the scan of a line and writing the picture signal to a memory of the other side in that period.

CONSTITUTION: The electric charge is stored in a fixed time shorter than 1/2 read-out scan time and then read out of a CCD1 in the same time. A switch 13 conducts only in the timing when picture signals equivalent to a line are read out of the CCD. Then the picture signals are led to memories 11 and 12 to be written to these memories for each line and then read out at a prescribed read- out scanning speed after a 1-line period. Therefore the preceding line is read out of the memory 12 while a line is written to the memory 11, and the next one line which is stored and delivered in the next period is written to the memory 12 while the memory 11 is read out. As a result, it is possible to control the storage and transfer of electric charge of the CCD1 independently of the read-out scanning speed. In addition, a fixed charge store time can be obtained regardless of the read-out scanning speed.