An optical dental caries diagnostic device comprising: a body unit having a predetermined length; a light-emitting member located in front of the body unit, the light-emitting member being configured to radiate visible light; and a power supply unit electrically connected to the light-emitting member, the power supply unit extending through the body unit and then being exposed at a rear of the body unit, wherein a filter unit detachably coupled to the light-emitting member is provided in front of the light-emitting member, wherein the filter unit comprises: a filter frame formed in a cylindrical shape having a predetermined length, the filter frame being provided at an outer side surface thereof with a second concavo-convex portion; and an optical filter mounted to the filter frame, the optical filter being configured to selectively transmit only light having a wavelength band of 405 to 410 nm; wherein the light-emitting member is connected to the body unit so as to be turnable at a predetermined angle therefrom; characterized in that the body unit comprises: a first body having a first sealed surface provided at an end of one side thereof, the first body having a hollow cylindrical shape; a second body having a smaller inner diameter than the first body, the second body being formed in a cylindrical shape having open opposite ends and an empty interior; a cylindrical connection member having an outer side surface disposed in tight contact with an inner surface of an edge of the outer side of the first body and an inner side surface located at an outer surface of the second body; and a control member located in an inner space of an edge of the one side of the first body, the control member being configured to control turning of the light-emitting member. a body unit having a predetermined length; a light-emitting member located in front of the body unit, the light-emitting member being configured to radiate visible light; and a power supply unit electrically connected to the light-emitting member, the power supply unit extending through the body unit and then being exposed at a rear of the body unit, wherein a filter unit detachably coupled to the light-emitting member is provided in front of the light-emitting member, wherein the filter unit comprises: a filter frame formed in a cylindrical shape having a predetermined length, the filter frame being provided at an outer side surface thereof with a second concavo-convex portion; and an optical filter mounted to the filter frame, the optical filter being configured to selectively transmit only light having a wavelength band of 405 to 410 nm; a filter frame formed in a cylindrical shape having a predetermined length, the filter frame being provided at an outer side surface thereof with a second concavo-convex portion; and an optical filter mounted to the filter frame, the optical filter being configured to selectively transmit only light having a wavelength band of 405 to 410 nm; wherein the light-emitting member is connected to the body unit so as to be turnable at a predetermined angle therefrom; characterized in that the body unit comprises: a first body having a first sealed surface provided at an end of one side thereof, the first body having a hollow cylindrical shape; a second body having a smaller inner diameter than the first body, the second body being formed in a cylindrical shape having open opposite ends and an empty interior; a cylindrical connection member having an outer side surface disposed in tight contact with an inner surface of an edge of the outer side of the first body and an inner side surface located at an outer surface of the second body; and a control member located in an inner space of an edge of the one side of the first body, the control member being configured to control turning of the light-emitting member. a first body having a first sealed surface provided at an end of one side thereof, the first body having a hollow cylindrical shape; a second body having a smaller inner diameter than the first body, the second body being formed in a cylindrical shape having open opposite ends and an empty interior; a cylindrical connection member having an outer side surface disposed in tight contact with an inner surface of an edge of the outer side of the first body and an inner side surface located at an outer surface of the second body; and a control member located in an inner space of an edge of the one side of the first body, the control member being configured to control turning of the light-emitting member.