Operation amount detection device

An operation amount detection device comprising:

• a first member configured to rotate about a rotation center axis by an operation force input to a pedal and transmit a rotation torque;
• a second member configured to receive, from a reaction force member, a reaction force of the rotation torque transmitted from the first member, the second member being rotatable about the rotation center axis and movable relative to the first member in an axial direction of the rotation center axis, and being interposed between the first member and the reaction force member;
• a conversion mechanism configured to convert rotation of the first member into a relative movement of the first member and the second member in the axial direction to convert the rotation torque into a thrust force which is a force in the axial direction;
• an elastic body provided apart from the reaction force member and configured to be elastically deformed by the thrust force;
• and
• a detection element fixed to the elastic body and configured to detect a deformation amount of the elastic body.