An image forming apparatus includes conveying device for conveying a printing medium in the substantially horizontal direction in the printing range where a printing agent is applied to the printing medium while a printing plane of the printing medium orients in the upward direction, a printer section including a plurality of printing heads located opposite to a platen portion of the printing range for applying the printing agent to the printing medium in the downward direction so as to form printed images on the printing medium by activating the printing heads, and supporting device for slidably displacing the printer section relative to the platen portion in the conveying direction of the printing medium conveyed by the conveying device, between the position where the printer section is located opposite to the platen portion and the non-opposing position spaced away from the preceding position. With such construction, a maintenance service can easily be conducted for the conveying device.