A vehicular lamp includes a light guide body which can suppress the generation of irregular light emission effectively while enhancing the light utilization efficiency of light emitted from a light source. Within a horizontal plane, a rear surface of the light guide body comprises: a first entrance portion (20A1) configured to allow light emitted from the light source (22) to enter in such a way as to be refracted to the front; second entrance portions (20A2) situated at both sides and configured to allow light to enter in such a way as to be refracted sideways; and a pair of reflecting portions (20A3) at left and right sides configured to internally reflect light from the light source to the front, so as to enhance the light utilization efficiency. The first entrance portion is configured to allow light emitted from the light source to enter as diffuse light in the first horizontal plane, and the reflecting portions (20A3) are configured to reflect light as diffuse light in the first horizontal plane. Therefore, an area where the incident light from the first entrance portion reaches and an area where the internally reflected light from the reflecting portion reaches are allowed to overlap each other over a wide range on the front surface (20a) of the light guide body, a dark portion (D) is not generated.