rate for example 15 to 60 cycles the two views can be observed simultaneously if a display area of the monitor 17 is divided into two areas by the control unit 14 the two views can be observed without adding another monitor however since the outer sleeve 34 is rotated mechanically actually it is rather difficult to rotate at such a faster rate as shown in fig7 a shutter 40 is arranged at the end of optical head 13 in place of the polarizing plates 31 32 in the first embodiment and another shutter 41 is arranged at the upper side of the pipe 12 since other components are the same as the first embodiment they are omitted in fig7 if the shutters 40 41 are opened and closed alternatively at a faster rate and two monitors are prepared the front view and the side view can be observed almost simultaneously the alternating rate may be in a range of 15 to 60 cycles from a practical point the shutters 40 41 may be mechanical ones or liquid crystal shutters but the liquid crystal shutters are more preferable taking safety and easy maintenance into consideration since the diseased area can be observed from two different angles simultaneously this arrangement is very useful for endoscopic.