A reaction force output device includes a driving part configured to transmit a driving force of a motor to a driving member through a gear mechanism to drive the driving member, thereby outputting a force in a direction opposite to an operating direction of an operation element to the operation element operated by a driver; and a controller configured to determine a control amount applied to the driving part based on an input value supplied from an outside, wherein the controller gradually increases the control amount, maintains the control amount at a constant value and then increases the control amount stepwise when increasing the control amount according to the input value.