1. An image forming apparatus which receives image data from a host device by communication and forms an image based on the image data on a target, the image forming apparatus comprising: a communication unit which receives the image data by the communication with the host device; a storage unit which is able to store the received image data; an image forming unit which ejects a fluid, to overlap one partial image forming process with another partial image forming process, in performing of an image forming process of forming the image on the target by ejecting the fluid from nozzles on a portion of the target and performing a partial image forming process of forming a portion of the image based on the image data stored in the storage unit on the target plural times; a control unit which performs a parallel control for controlling the received image data to be stored in the storage unit and controlling the image forming unit to perform the image forming process when a communication velocity of the communication unit and the host device is greater than a predetermined reference velocity, and performs a serial control for controlling the received image data to be stored in the storage unit and controlling the image forming unit to perform the image forming process after the storage unit stores all the image data when the communication velocity of the communication unit and the image forming unit is less than the reference velocity.