An image pickup device for sensing a two-dimensional (2D) image while causing a projected image of an object to be sensed being projected onto a linear image sensor to relatively move with respect to the linear image sensor in a direction (V scanning) perpendicular to the internal scan (H scan) direction of the linear image sensor. This device includes a position detector circuit that detects the position of the object to be sensed, and a pixel size modifier circuit for changing or modifying the setup configuration of a pixel size in the V scan direction of the linear image sensor on the basis of a position detection signal indicative of the position of the to-be-sensed object as detected by the position detector circuit. The pixel size modifier circuit is operable based on the object position detection signal to periodically change the interval of H-scanning start pulses of the linear image sensor.