An illumination device for irradiating light on an object (W) in image measurement for performing an appearance inspection of the object (W), the illumination device comprising: an illumination unit for irradiating light on the object (W); a holding mechanism for detachably holding the illumination unit at a predetermined position of the illumination device according to predetermined disposition rule; and wherein the holding mechanism 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 , wherein the illumination unit comprises: a first illumination unit whose dominant wavelength to be irradiated is a first wavelength, and a second illumination unit 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 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 (W); a holding mechanism for detachably holding the illumination unit at a predetermined position of the illumination device according to predetermined disposition rule; and wherein the holding mechanism 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 , wherein the illumination unit comprises: a first illumination unit whose dominant wavelength to be irradiated is a first wavelength, and a second illumination unit 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 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 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 is held, characterized in that the identification mechanism (Ri) of the illumination unit is a resistor (Ri). <EOS>