PURPOSE: To make it possible to compute image data arrayed in the vertical direction by successively turning on switches at an interval of two switches by means of a switch control circuit in a shift register and arranging the positions of memories respectively storing vertical image data close to each other.

CONSTITUTION: Flip flops(FFs) 221 to 22M/2 and 241 to 24M/2 are provided to constitute a switch control circuit and signals from respective FFs are extracted through selectors 251 to 25M. When a signal is inputted from a switch ON signal input terminal 21, a switch control signal for turning on a 1st switch 21 is outputted from the FF 221 first because the FFs 221 to 22M/2 are cascade- connected, and then a switch control signal for turning on a 3rd switch 23 is outputted from the FF 222. Finally a switch control signal for turning on the (M-1)th switch 2M-1 is outputted from the FFM/2.