An image forming apparatus includes a skew correcting unit that performs skew correction by dividing an input image that has undergone a halftone process into image data in a predetermined skew correction area in a main scanning direction and by shifting the image data in the skew correction area in a sub-scanning direction; an edge detecting unit that detects whether a pixel at a division position is an edge pixel based on concentrations of a set of pixels including the pixel at the division position; a correction area determining unit that, if detected that the pixel at the division position is the edge pixel, determines a correction area that is an area of pixels including the edge pixel to be subjected to concentration correction within the skew correction area; and an edge correcting unit that corrects concentrations of the pixels within the correction area.