A through hole penetrating in a vertical direction and a slot which is separated from the through hole in the direction along the sheet surface and is long in a separating direction are provided on a light reflection sheet supported on a support body supporting a light source for reflecting light emitted from the light source, and there are provided a first shaft member fitted in the through hole for setting a position of the light reflection sheet with respect to the support body, and a second shaft member fitted in the slot to enable a relative movement in a longitudinal direction of the slot for setting the position of the light reflection sheet with respect to the support body.