An insertion instrument includes an insertion portion having a curving portion, and an operation portion body coupled to the proximal side of the insertion portion. The operation portion body includes a first surface, and a second surface extending from the first surface and extending in a direction different from the direction in which the first surface extends. A finger side other than a thumb of a grasping hand is located in the second surface. The operation portion body includes a first curving operation portion which is provided in the first surface and which curves the curving portion in a first direction, a functional switch which is provided in the second surface and which operates a predetermined function of the insertion instrument, and a second curving operation portion which is provided in the second surface.