To suppress degradation of an image quality due to deviation of a medium from a conveyance roller.

The printer executes a printing method which switches from a normal process to a transition process before an image formation operation immediately after a conveyance operation where a lower end deviates from the conveyance roller and which switches from the transition process to a lower end process. A first position which is a position on the medium of a dot train formed by use nozzles in each image formation operation is allocated to the use nozzles of each image formation operation. The printer searches use nozzles to which the same position as the first position allocated to use nozzles of the image formation operation immediately after deviation from the conveyance roller is allocated among use nozzles of the normal process, use nozzles of the transition process and use nozzles of the lower end process, and distributes and assigns pixel data.