PURPOSE: To shorten the position detecting time by deciding a scan area near a position indicated by an input pen after detecting the shift speed and the shift direction of the input pen.

CONSTITUTION: A coordinate detector consists of a coordinate input board 1, a scan circuit 2, an A/D converter 5 and an arithmetic control part 6. The circuit 2 is driven by a CPU10 of the part 6 for a prescribed scan period via a timer 12, a sampling timer 11, etc. In this case, the starting point is decided for the scan of the board 1 based on the coordinate value indicated by an input pen as well as the shift speed and direction of the pen and by means of registers 16W 20 of the part 6 and fixed value setting devices 21W33 for reference speed. Then the partial areas are scanned for a prescribed number of coordinate lines. Thus a scan area is decided according to the shift speed and direction of the input pen. While the entire area of the board 1 is scanned when the input pen is detached from the board 1. This ensures the detection of coordinates with the satisfactory follow-up performance.