PURPOSE: To make possible observing the images of plural different planes simultaneously and distinctly or indiscretely through specification of arbitrary positions by providing a multifocus element whose refractive indices vary with the deflecting direction of light between the objective lens and the observing object plane.

CONSTITUTION: For example, a uniaxial crystal plate 3 of a thickness t is provided between an objective lens 2 and its focal position, i.e., image plane 8a. The optical axis of the crystal plate 3 is set perpendicularly to the optical axis center of the objective lens 2, i.e., the device center axis 4. On the other hand, a light source 5 is disposed in the position below the objective lens 2 to light the deflecting plate through a condenser lens 6. The vibrating direction of this deflecting plate 7 is determined in the direction perpendicular to the axial direction of the central axis 4 and is so arranged as to be rotated from the arrow A direction to the direction perpendicular to the plane of the figure by a rotating device. The uniaxial crystal plate 3 changes its refractive indices ω, with the deflecting rays of the deflecting plate 7 and its image plane becomes 8c, 8b. Namely, if the deflecting plate 7 is continuously rotated about the central axis 4, the focus position changes continuously in the range between the image planes 8b, 8c.