[Object] It is an object to provide a method for forming a three-dimensional object that suppresses generation of streaks on the three-dimensional object, which streaks are parallel to a main scanning direction.[Means of Realizing the Object] A method for forming a three-dimensional object includes a slice information calculation step (step ST23) of dividing three-dimensional data of the three-dimensional object into a plurality of layers so as to calculate cross-sectional slice information of each of the layers; and a unit-layer formation step (step ST27) of forming each of the layers based on the cross-sectional slice information. The unit-layer formation step (step ST27) is repeated a plurality of times. The unit-layer formation step (step ST27) includes a printing step (step ST27A) of extruding inks onto a work surface while moving the extruders in the main scanning direction so as to form a single print path. The printing step and a sub-scanning direction movement step (step ST27B) of moving the work surface in a sub-scanning direction are alternately performed. The print paths are formed in such a manner that a boundary between the print paths between each adjacent pair of layers in a deposition direction of the layers is at least partly deviated in the sub-scanning direction.