A reflecting device (1, 2, 3, 4, 5, 6), comprising: an oscillation part, comprising: a mirror part, supported on a support frame; and a hinge part, engaging the mirror part and the support frame, wherein the mirror part oscillates with respect to the support frame, the hinge part has a tensile strength of 1500 MPa or higher, a mass M [mg]. of the mirror part and a resonance frequency f 0 [kHz], of the oscillation part satisfy relational expression below, 0.49 * f 0 + 6.23 ≤ M ≤ 43. 68*f 0 − 3.12 wherein the oscillation part is formed to be symmetrical with respect to a central axis of the mirror part and the hinge part being extended from a middle portion of left and right lateral surfaces of the mirror part, and is engaged with an inside of the support frame, wherein the reflective device is characterized in that, the mirror part includes a metal part and a reflecting part joined with the metal part; a reflecting layer is formed on a top surface of the reflecting part; the reflecting part is joined and fixed to a part of the metal part, and the mirror part other than the part of the metal part is thinned which is a thinning part (16, 142, 142a, 142b, 142c, 142d, 144a, 144b, 146a, 146b) formed on a surface different from a reflecting surface of the mirror part; the metal part has a fixing part for fixing an electromagnetically driving magnet to the mirror part, wherein the electromagnetically driving magnet generates a driving force that oscillates the oscillation part using a coil provided to face the electromagnetically driving magnet; and the thinning part (16, 142, 142a, 142b, 142c, 142d, 144a, 144b, 146a, 146b) is around the fixing part. a mirror part, supported on a support frame; and a hinge part, engaging the mirror part and the support frame, wherein the mirror part oscillates with respect to the support frame, the hinge part has a tensile strength of 1500 MPa or higher, a mass M [mg]. of the mirror part and a resonance frequency f 0 [kHz], of the oscillation part satisfy relational expression below, 0.49 * f 0 + 6.23 ≤ M ≤ 43. 68*f 0 − 3.12 wherein the oscillation part is formed to be symmetrical with respect to a central axis of the mirror part and the hinge part being extended from a middle portion of left and right lateral surfaces of the mirror part, and is engaged with an inside of the support frame, wherein the reflective device is characterized in that, the mirror part includes a metal part and a reflecting part joined with the metal part; a reflecting layer is formed on a top surface of the reflecting part; the reflecting part is joined and fixed to a part of the metal part, and the mirror part other than the part of the metal part is thinned which is a thinning part (16, 142, 142a, 142b, 142c, 142d, 144a, 144b, 146a, 146b) formed on a surface different from a reflecting surface of the mirror part; the metal part has a fixing part for fixing an electromagnetically driving magnet to the mirror part, wherein the electromagnetically driving magnet generates a driving force that oscillates the oscillation part using a coil provided to face the electromagnetically driving magnet; and the thinning part (16, 142, 142a, 142b, 142c, 142d, 144a, 144b, 146a, 146b) is around the fixing part.