1. An image forming apparatus comprising: an image forming section that forms an image on an object, the object being movable in a moving direction; a controlling section that controls the image forming section to form a calibration pattern on the object, the calibration pattern including a plurality of first patterns for correcting an image forming position in a first direction and a plurality of second patterns for correcting an image forming position in a second direction different from the first direction, each of the plurality of first patterns including at least one pair of marks, each of the at least one pair of marks having different colors and overlapping with each other in the first direction, the plurality of first patterns having different degrees of overlapping from each other, each of the plurality of second patterns being formed between one of the plurality of first patterns and another one of the plurality of first patterns in the moving direction thereby forming a combined pattern; a detecting section that detects the plurality of first patterns and the plurality of second patterns formed on the object, thereby obtaining detection results; and a correcting section that corrects the image forming position in the first direction based on the detection results of the plurality of first patterns, and that corrects the image forming position in the second direction based on the detection results of the plurality of second patterns.