A backlight device includes a housing, a light source, a diffuse plate and a fixing member. The housing has an open surface. The light source is arranged in the housing. The diffuser plate is arranged on the open surface of the housing and allows light emitted from the light source to pass therethrough while diffusing the light. The fixing member prevents the diffuser plate from bending in a direction in which light passes through the diffuser plate. A part of the fixing member has transmittance adjusted to substantially equalize luminance distribution of light passed through the diffuser plate.