An image forming apparatus includes a pick-up unit configured to pick up a printing medium stored in a printing medium storage unit and transport the picked printing medium to a printing medium transportation path provided inside a body, the pick-up unit having a pick-up roller to pick up the printing medium in the printing medium storage unit and a forward roller to guide the picked-up printing medium, to the printing medium transportation path, and the body including a guide portion slantingly extending from a lower side of the forward roller toward one side of the forward roller to guide the picked-up printing medium, and a plurality of locking protrusions protruding from the guide portion to prevent a plurality of printing media from being simultaneously entered to a gap between the forward roller and the guide portion.