An image reducing unit performs a reduction process for each reduction target area in one of a primary scanning direction and a secondary scanning direction, and subsequently performs a reduction process for each reduction target area in the other of the primary scanning direction and the secondary scanning direction. A binarizing unit binarizes pixel values of pixels in the reduction target area. A characteristic value identifying unit identifies a characteristic value on the basis of a pattern of the binarized pixel values and integrates the characteristic value. When the integrated value of the characteristic value exceeds a threshold value before the image reduction unit finishes the reduction processes, a control unit terminates the reduction process, changes the reduction ratio so as to increase a size of a reduced image, and causes the image reducing unit to perform the reduction process with the changed reduction ratio again.