An illumination device for irradiating light on an object in image measurement for performing an appearance inspection of the object, the illumination device comprising: an illumination unit for irradiating light on the object; a holding mechanism (24, 68) for detachably holding the illumination unit at a predetermined position of the illumination device according to predetermined disposition rule; and wherein the holding mechanism (24, 68) of the illumination device comprises a substrate member provided with a plurality of linking parts being provided on the substrate member, each of the linking parts being detachably linked to a connection part of the illumination unit, the connection part functioning as end part of the illumination unit, and wherein the end part is provided at a position different from a light emitting surface of the illumination unit, the substrate member having a further connection part for electrically connecting with a controller which is configured to perform a lighting control of the illumination unit held by the holding mechanism (24, 68), wherein the illumination unit comprises: a first illumination unit whose dominant wavelength to be irradiated is a first wavelength, and a second illumination unit (6g, 6b) whose dominant wavelength to be irradiated is a second wavelength different from the first wavelength, and wherein the illumination unit further comprises an identification mechanism (R i) for identifying which illumination unit among the first illumination unit and the second illumination unit (6g, 6b) is held, characterized in that the identification mechanism (Ri) of the illumination unit is a resistor (Ri). an illumination unit for irradiating light on the object; a holding mechanism (24, 68) for detachably holding the illumination unit at a predetermined position of the illumination device according to predetermined disposition rule; and wherein the holding mechanism (24, 68) of the illumination device comprises a substrate member provided with a plurality of linking parts being provided on the substrate member, each of the linking parts being detachably linked to a connection part of the illumination unit, the connection part functioning as end part of the illumination unit, and wherein the end part is provided at a position different from a light emitting surface of the illumination unit, the substrate member having a further connection part for electrically connecting with a controller which is configured to perform a lighting control of the illumination unit held by the holding mechanism (24, 68), wherein the illumination unit comprises: a first illumination unit whose dominant wavelength to be irradiated is a first wavelength, and a second illumination unit (6g, 6b) whose dominant wavelength to be irradiated is a second wavelength different from the first wavelength, and wherein the illumination unit further comprises an identification mechanism (R i) for identifying which illumination unit among the first illumination unit and the second illumination unit (6g, 6b) is held, characterized in that the identification mechanism (Ri) of the illumination unit is a resistor (Ri). a first illumination unit whose dominant wavelength to be irradiated is a first wavelength, and a second illumination unit (6g, 6b) whose dominant wavelength to be irradiated is a second wavelength different from the first wavelength, and wherein the illumination unit further comprises an identification mechanism (R i) for identifying which illumination unit among the first illumination unit and the second illumination unit (6g, 6b) is held, characterized in that the identification mechanism (Ri) of the illumination unit is a resistor (Ri).