An illumination device (1, 100) comprising: a light guide plate (40, 140, 240); and multiple light emitting elements annularly arranged on a back side of the light guide plate, wherein the light guide plate comprises: an element array-facing part (44, 144) which is a part facing an element array of the multiple light emitting elements and which has an incident surface (44b, 144b) to allow light emitted from the light emitting elements to enter; an inner reflecting part (45, 145, 245) which is located on an inner side of the element array-facing part and has a reflecting surface for reflecting the light entering from the incident surface toward the inner side of the element array-facing part; and an annular inner part (42, 142) formed on an inner side of the inner reflecting part continuously with the inner reflecting part, characterized in that the inner reflecting part (45, 145, 245) has a first light scattering region (45b, 145b, 245b) having a light scattering treatment applied thereto, the annular inner part (42, 142) comprises a third light scattering region (42b, 142b) having a light scattering treatment applied thereto, recesses (42c, 45c, 142c, 145c, 245c) and/or projections are provided in the first light scattering region and the third light scattering region as the light scattering treatment, and a density of the recesses and/or projections decreases from the first light scattering region toward the third light scattering region. a light guide plate (40, 140, 240); and multiple light emitting elements annularly arranged on a back side of the light guide plate, wherein the light guide plate comprises: an element array-facing part (44, 144) which is a part facing an element array of the multiple light emitting elements and which has an incident surface (44b, 144b) to allow light emitted from the light emitting elements to enter; an inner reflecting part (45, 145, 245) which is located on an inner side of the element array-facing part and has a reflecting surface for reflecting the light entering from the incident surface toward the inner side of the element array-facing part; and an annular inner part (42, 142) formed on an inner side of the inner reflecting part continuously with the inner reflecting part, characterized in that the inner reflecting part (45, 145, 245) has a first light scattering region (45b, 145b, 245b) having a light scattering treatment applied thereto, the annular inner part (42, 142) comprises a third light scattering region (42b, 142b) having a light scattering treatment applied thereto, recesses (42c, 45c, 142c, 145c, 245c) and/or projections are provided in the first light scattering region and the third light scattering region as the light scattering treatment, and a density of the recesses and/or projections decreases from the first light scattering region toward the third light scattering region. an element array-facing part (44, 144) which is a part facing an element array of the multiple light emitting elements and which has an incident surface (44b, 144b) to allow light emitted from the light emitting elements to enter; an inner reflecting part (45, 145, 245) which is located on an inner side of the element array-facing part and has a reflecting surface for reflecting the light entering from the incident surface toward the inner side of the element array-facing part; and an annular inner part (42, 142) formed on an inner side of the inner reflecting part continuously with the inner reflecting part, characterized in that the inner reflecting part (45, 145, 245) has a first light scattering region (45b, 145b, 245b) having a light scattering treatment applied thereto, the annular inner part (42, 142) comprises a third light scattering region (42b, 142b) having a light scattering treatment applied thereto, recesses (42c, 45c, 142c, 145c, 245c) and/or projections are provided in the first light scattering region and the third light scattering region as the light scattering treatment, and a density of the recesses and/or projections decreases from the first light scattering region toward the third light scattering region.