To precisely measure deflection characteristics of a mirror system capable of changing the tilting of a mirror surface, in a short time.

The measurement device includes a measurement light source 14 for irradiating the mirror surface with a measurement light; a concave surface projection section 20-1 including the projection surface 20a-1 of a concave surface shape, reflecting the light obtained by reflecting the measurement light emitted from the measurement light source 14 by the mirror surface; a light-receiving section 191 receiving the reflected light in the projection surface of the concave surface projection section 20-1; and a measurement section 104 measuring the characteristics of a mirror system, on the basis of the light received by the light receiving section 191.