The present invention aims at providing a mirror device, comprising a plurality of mirror elements, wherein each of the mirror elements comprises a deflectable mirror, and an elastic member for deflectably supporting the mirror, wherein the mirror allows to be controlled under a first deflection control state in which incident light is reflected toward a first direction, a second deflection control state in which the incident light is reflected toward a second direction, and a third deflection control state in which the mirror oscillates between the first deflection control state and second deflection control state, wherein the mirror device reproduces gradations by combining the first through third deflection control states, and the natural oscillation cycle T of the oscillation system constituted by the mirror and elastic member satisfies: 110 [.mu.sec]>T=2.pi.* (I/K)>2 [.mu.sec], where "I" is the moment of rotation of the oscillation system and "K" is the spring constant of the elastic member.