A position error correcting method includes forming an image-forming condition determination pattern on an endless transport unit transported in a first direction, the image-forming condition determination pattern including plural unit patterns having different unit-area attached toner amounts and arranged in the first direction; detecting a detection limit pattern having the minimum detectable unit-area attached toner amount from the unit patterns; calculating an image-forming condition of the detection limit pattern; forming a position error correction pattern on the endless transport unit in the first direction in accordance with the image-forming condition; and correcting a position error of a toner image formed on the endless transport unit by plural image forming units, using the position error correction pattern, wherein the position error is corrected with respect to a second direction perpendicular to the first direction.