An illumination device includes a light source, a first optical member, and a fixing portion. The first optical member includes a light reflection portion configured to reflect light, at least a part of the light reflection portion overlapping with the light source, and a light transmitting portion configured to transmit light, the light transmitting portion not overlapping the light reflection portion. A center of the light source in a plan view is defined as a first center, and a center of the light reflection portion in a plan view is defined as a second center. In the light reflection portion, the second center is located between the fixing portion and the first center at a first temperature, and at a second temperature higher than the first temperature, a position of the second center is closer to the first center than a position of the second center at the first temperature.