A derailleur comprises a base member configured to be attached to a human-powered vehicle frame, a movable member movable with respect to the base member, a pulley assembly pivotally attached to the movable member in a first pivotal direction and a second pivotal direction opposite to the first pivotal direction and including a first pulley having a first pulley axis and a second pulley having a second pulley axis, a pulley assembly biasing member configured to bias the pulley assembly with respect to the movable member in the first pivotal direction, a pulley distance (centimeter) being defined between the first pulley axis and the second pulley axis, a biasing return force (newton) being defined by rotational force of the pulley assembly relative to the movable member, and a return value defined by the biasing return force multiplied by the pulley distance. The return value is 136 or larger.