A bending angle adjustment mechanism for an endoscope for adjusting a maximum bending angle of a bending portion, the bending angle adjustment mechanism being provided in a bending operation mechanism for moving the bending portion by rotation of a knob attached to a rotating shaft provided at an operation portion which is held to be operated by an operator, to rotate a rotating wheel attached to the rotating shaft and to reciprocally move a long member which is connected with wires extending from the bending portion at a distal end of an insertion portion and wound around the rotating wheel, wherein the bending angle adjustment mechanism comprises: a rod member that is provided to extend in a longitudinal direction of the insertion portion, and has a threaded portion formed on a surface in a longitudinal direction thereof; a plate member that is provided to be parallel to the longitudinal direction of the rod member and through which the rod member is inserted at both ends curved in a substantially perpendicular direction; an adjustment piece that is screwed onto the threaded portion of the rod member and positioned in the threaded portion; a guide member that has a portion sandwiched and fixed by the rod member and the plate member, and is disposed to be parallel to the rod member and the plate member and provided with a guide path (53xa, 53xb) for guiding a position of the adjustment piece in the longitudinal direction of the insertion portion; characterized in that the bending angle adjustment mechanism comprises a convex portion that is provided in the guide member, wherein a protruding amount of the convex portion is set so that the convex portion protrudes to be higher than a lower edge position of an outer circumferential edge portion of a head portion of the rod member, in a state in which the rod member is disposed in a normal position in the bending angle adjustment mechanism, that is formed to have elasticity so that the head portion of the rod member is allowed to ride over the convex portion when the rod member is inserted into the plate member along the axial direction of the rod member and, when the outer circumferential edge portion of the head portion abuts on the convex portion, is adapted to prevent the rod member from falling off from the plate member while keeping the head portion of the rod member which is supported by the plate member in a rotatable state. a rod member that is provided to extend in a longitudinal direction of the insertion portion, and has a threaded portion formed on a surface in a longitudinal direction thereof; a plate member that is provided to be parallel to the longitudinal direction of the rod member and through which the rod member is inserted at both ends curved in a substantially perpendicular direction; an adjustment piece that is screwed onto the threaded portion of the rod member and positioned in the threaded portion; a guide member that has a portion sandwiched and fixed by the rod member and the plate member, and is disposed to be parallel to the rod member and the plate member and provided with a guide path (53xa, 53xb) for guiding a position of the adjustment piece in the longitudinal direction of the insertion portion; characterized in that the bending angle adjustment mechanism comprises a convex portion that is provided in the guide member, wherein a protruding amount of the convex portion is set so that the convex portion protrudes to be higher than a lower edge position of an outer circumferential edge portion of a head portion of the rod member, in a state in which the rod member is disposed in a normal position in the bending angle adjustment mechanism, that is formed to have elasticity so that the head portion of the rod member is allowed to ride over the convex portion when the rod member is inserted into the plate member along the axial direction of the rod member and, when the outer circumferential edge portion of the head portion abuts on the convex portion, is adapted to prevent the rod member from falling off from the plate member while keeping the head portion of the rod member which is supported by the plate member in a rotatable state.