To miniaturize a derailleur which is integrated with a motor.

This derailleur for bicycle is equipped with a base member, a movable member which supports a chain guide, a first link member 120 which is connected with the base member and the movable member respectively through first and second link pins 128 and 138, a second link member 124 which is connected with the base member and the movable member respectively through third and fourth link pins 146 and 154, and the motor having a driving shaft which forms a driving shaft vector V. The first to fourth link pins constitute edges of a virtual space 250, and continuous straight lines PH1 to PH8, which connect the end sections of the first to fourth link pins and do not cross, constitute the remaining edges of the virtual space. At least a part of a main motor housing 214 is arranged in the virtual space. Also, the driving shaft vector faces the direction separating from a surface including the second and fourth link pins.