PURPOSE: To provide the paper discharge opening switching device of an image forming device enabling positive paper discharge dispensing with manual discharge opening changeover.

CONSTITUTION: In an image forming device transfer paper 13 delivered from a paper supply part 1 is conveyed to a transfer part 5 through a carrier path 2 to be subjected to transfer and then to fixing at a fixing part 6, and discharged into a paper discharge path 7 so as to be stored in paper discharge trays 10, 11. The discharge path 7 into which the fixed transfer paper 13 is discharged is branched into at least two branch discharge paths 8a, 8b. The discharge trays 10, 11 are respectively disposed at these branch discharge paths 8a, 8b. A branch path switching means 9 is provided at a branch point P between the paper discharge path 7 and the branch discharge paths 8a, 8b, and branch path changeover interlocking mechanism 12 is provided to switch the branch path switching means 9 interlockingly with the installation action of one discharge tray 11.