An endoscope operation portion structure includes: an operation portion main body 23 which includes a rectangular opening portion 24a and a plurality of screw receiving portions 61 to 63 and a frame member 40 to be inserted from the opening portion 24a into the operation portion main body 23 and including a plurality of fixing portions 41 to 43 fixed to the plurality of screw receiving portions 61 to 63 with fixing members 51, wherein two fixing portions 42, 43 among the plurality of fixing portions 41 to 43 are formed so as to protrude from different side portions of the frame member 40 in directions away from the frame member, the directions being perpendicular to a longitudinal direction of the frame member, and lengths L1, L2 in a width direction perpendicular to the longitudinal direction of the frame member 40 are longer than a length L4 of a long side direction of the opening portion 24a, and shorter than a length L5 of a diagonal direction of the opening portion.
