The present invention provides for example a reflecting mirror that has a reflecting surface that is capable or preventing the rise of the temperature of the electrodes due the reflection light. The reflecting surface that reflects towards the electrodes the light rays emitted by the lamp has been corrected such that within an area surrounded by line segments connecting points P1(Z1, Y1), P2(Z2, Y2) and P3(Z3, Y3) and a Z axis, a part Sp corresponding to a distance between the electrodes is enlarged, wherein on a Z-Y rectangular coordinate system defined with a common axis as the Z-axis and an axis intersecting the Z-axis at a right angle at a center point (C) between the electrodes as a Y-axis, Z coordinates of the points P1(Z1, Y1), P2(Z2, Y2) and P3(Z3, Y3) respectively represent positions of intersection points with the Z-axis of reflection lights which have been emitted from 1st to 3rd points arranged in the common axis in number order and have been reflected at an identical reflection point on the reflecting mirror, and Y coordinates thereof respectively represent illuminances at the intersection points.