A rear under mirror that is placed near a top edge portion of a rear window glass on a vehicle compartment interior side thereof, the rear under mirror including: a reflecting mirror that reflects a lower area behind a vehicle towards a driver's seat, the reflecting mirror comprising a concavo-convex mirror having a mirror surface that is formed as a concave surface in a substantially vertical direction and as a convex surface in a substantially horizontal direction, the reflecting mirror having a radius of curvature of the convex surface in a substantially horizontal direction of the reflecting mirror in the bottom portion area is larger than that of the top portion area, the reflecting mirror having a trapezoidal shape whose bottom side is longer than top side when viewed from a front thereof.