To provide a color slippage correcting method which accurately determines the position relations between sensor chips with due consideration given to assembly errors to correct color slippage, and to provide an image reader.

A color slippage correction chart 1 with colors different in a scanning direction is prepared. A color image sensor scans the color slippage correction chart 1 to at least one direction of a main scanning direction or an auxiliary direction. In this color slippage method, color slippage correction is executed based on the slippage of the recognition timing of a color change with respect to the color slippage correction chart 1 between sensor chips at the scanning.