A light guide includes a first incident portion at an end side thereof near a light source, a stepped portion disposed on a rear surface side thereof in an axial direction and wholly reflects a portion of guided light, and a radiating portion disposed on a front surface side thereof in the axial direction that radiates the wholly reflected light forward. The light guide guides light that is incident through the first incident portion from front to back within the light guide. The stepped portion is a plurality of generally triangular prisms formed continuous in an extension direction, and has, in a cross section that follows an extension axis of the light guide and is parallel to a lamp optical axis, a long first projection surface that extends in the extension direction and a short second projection surface that forms an apex angle with the first projection surface.