To eliminate the brightness irregularity caused because a part of a double semi-ellipse is missing.

The reflection mirror 3 for backlight has such a shape that two semi-ellipses prepared by dividing contours of two ellipses 31, 32 which jointly own one focus 10 with a straight line containing the owned focus 10 and other two focuses 21, 22 are arranged side by side, wherein a protrusion part 34 is disposed so as to cover an intersection 37 of two divided semi-ellipses. The brightness is uniformized by directing reflection light 54 to the boundary position 61 with the protrusion part 34.