A multidirectional simultaneous observation optical system is composed of, as shown in FIG. 2, side image acquiring prism systems (145A, 145B) and so forth for acquiring side images of an object (11) and bottom image acquiring prism system (185F) for acquiring a bottom image. The prism system (145A) and so forth include optical path direction changing prisms (14A, 14B, 18F) and so forth respectively. An open space for acquiring the top image is defined directly above the object (11). The optical paths of the light beams emerging from the prism system (145A) and so forth extend upward from the object (11), and are so disposed as not to be blocked by the other prism systems. As a result, the object can be accurately observed from various directions simultaneously.