A reflection mirror has reflection steps formed as portions of respective paraboloids of revolution and disposed between adjacent ones of closed curves formed as lines of intersection of a group consisting of the paraboloids of revolution with different focal distances and a fundamental surface for the reflection surface. The fundamental surface for the reflection surface includes a first curved surface portion and a second curved surface portion connected to the first curved surface portion in the n-th order continuity (N.gtoreq.1). The first curved surface portion is shaped such that when a light beam, which is emitted from a point light source supposed to lie on the principal optical axis of the reflection mirror, is reflected at a reflection point on the first curved surface portion, the light beam reflected thereat is directed substantially parallel to the principal optical axis of the reflection mirror. The second curved surface portion is shaped such that when a light beam, which is emitted from the point light source, is reflected at a reflection point on the second curved surface portion, the light beam reflected thereat is diffused in a given direction.