An illumination optical system unit for an endoscope comprising: an optical fiber (39A, 39B) that guides laser light supplied from a laser light source to a tip thereof and emits the laser light; a fluorescent body that is excited by the laser light emitted from the optical fiber (39A, 39B) and emits fluorescent light and forms white light formed of the fluorescent light and the laser light; a holding member including a fluorescent body-holding portion of which a tip side is opened and which holds the fluorescent body and a through hole which continues to a base end of the fluorescent body-holding portion and into which the optical fiber is inserted, at least a part of the holding member being formed of a magnetic body; a sleeve member (61, 62) of which a tip and a base end are opened and into which the holding member is fitted, the optical fiber (39A, 39B) protruding from the base end of the sleeve member (61, 62); a protective cover (38, 81, 86) that covers a tip side of the fluorescent body and allows the fluorescent light and the laser light to be transmitted therethrough; a first sealing portion that is formed by the adhesion between the protective cover and the sleeve member and seals the tip side of the fluorescent body; characterized by a second sealing portion that allows the holding member and the sleeve member (61, 62) to adhere to each other so that a tip of the holding member is allowed to come into close contact with the protective cover (38, 81, 86) by biasing the holding member toward the protective cover by magnetic force after the protective cover (38, 81, 86) and the sleeve member (61, 62) are adhered to each other, and seals a base end side of the fluorescent body. an optical fiber (39A, 39B) that guides laser light supplied from a laser light source to a tip thereof and emits the laser light; a fluorescent body that is excited by the laser light emitted from the optical fiber (39A, 39B) and emits fluorescent light and forms white light formed of the fluorescent light and the laser light; a holding member including a fluorescent body-holding portion of which a tip side is opened and which holds the fluorescent body and a through hole which continues to a base end of the fluorescent body-holding portion and into which the optical fiber is inserted, at least a part of the holding member being formed of a magnetic body; a sleeve member (61, 62) of which a tip and a base end are opened and into which the holding member is fitted, the optical fiber (39A, 39B) protruding from the base end of the sleeve member (61, 62); a protective cover (38, 81, 86) that covers a tip side of the fluorescent body and allows the fluorescent light and the laser light to be transmitted therethrough; a first sealing portion that is formed by the adhesion between the protective cover and the sleeve member and seals the tip side of the fluorescent body; characterized by a second sealing portion that allows the holding member and the sleeve member (61, 62) to adhere to each other so that a tip of the holding member is allowed to come into close contact with the protective cover (38, 81, 86) by biasing the holding member toward the protective cover by magnetic force after the protective cover (38, 81, 86) and the sleeve member (61, 62) are adhered to each other, and seals a base end side of the fluorescent body.