An image forming apparatus which is capable of adjusting the color density while improving the printing efficiency. A color density adjustment value-adjusting unit adjusts a color density adjustment value in predetermined adjustment timing so as to keep colors of an image constant. A color density adjustment value-storing unit stores the color density adjustment value in advance. An adjustment timing occurrence-determining unit determines whether or not the adjustment timing occurs during execution of an image forming job. A color density adjustment value-predicting unit predicts the color density adjustment value in the adjustment timing determined to occur, based on the color density adjustment value stored in advance. The color density adjustment value-adjusting unit is adapted to adjust the color density adjustment value based on the predicted color density adjustment value.