To provide an opening/closing detection mechanism capable of detecting an open/closed state of three opening/closing parts provided on neighboring three surfaces of a casing, and to provide an image forming apparatus with the same.

The opening/closing detection mechanism 70 detects opening/closing of panels 10P, 10F, 10R on surfaces, neighboring to each other, of the casing. While the panel 10F is closed, a member 71 to be detected is supported on the panel 10F so as to be rotated from a predetermined position near upper and right side surfaces to an upper surface side and to a right side surface side. A torsion spring 73 energizes the member 71 to be detected to the right side surface side. A torsion spring 74 energizes the member 71 to be detected to the upper surface side. When the panel 10R is closed while the panels 10P, 10F are closed, an abutting part 75 rotates the member 71 to be detected to a predetermined position. When the panel 10P is closed while the panels 10F, 10R are closed, an abutting part 76 rotates the member 71 to be detected to the predetermined position. A detecting part 77 detects that the member 71 to be detected is located at the predetermined position.