In the invention, an inclination amount of sensors is reflected in positional deviation correction patterns, and for correcting formation positions of images of various colors, the positional deviation correction patterns are formed on a conveying belt. The positional deviation correction patterns are detected by the sensors. A control unit calculates positional deviation correction amounts based on detection results of the positional deviation correction patterns. Based on the calculated positional deviation correction amounts, the control unit performs calculation for correcting the positional deviation correction patterns, and cancels the inclination amount reflected in the calculation results to obtain final positional deviation correction amounts. Skew correction is performed based on the final positional deviation correction amounts, and thus, the positional deviations are corrected.