An operation apparatus mountable to one hand of a user includes: a first operation section that is located on a front surface side and that can be operated by the thumb of the one hand; a second operation section that is located on a back surface side and that can be operated by a finger other than the thumb; and a first contact surface with which the palm of the one hand makes contact. At least one of the first contact surface and an extension plane of the first contact surface is inclined relative to a virtual plane in such a direction as to be spaced more therefrom in going in a first direction, the virtual plane being defined by the first direction from the front surface side toward the back surface side and a second direction being orthogonal to the first direction and directed from a bottom surface side toward a top surface side.