PURPOSE: To prevent erroneous observation and vertical or horizontal erroneous recognition of a part to be observed by providing a gravity direction detecting means to output a signal indicating a direction of gravity at an inserting section.

CONSTITUTION: When an object reflects an illumination light, the reflected light thereof forms an image on an imaging surface of a solid image sensor 19 through an objective optical system 18. The solid image sensor 19 converts an optical image formed into an electrical signal, which is sent to a video signal processing circuit 23 through a signal line 21. The video signal processing circuit 23 receives the electrical signal to be converted into a reference video signal, which is outputted to a video rotary processing circuit 25. On the other hand, a gravity direction detector 26 is fixed at a tip 11 of an endoscope and when the tip 11 parallels the ground, an electroconductive liquid 28 inside the detector 26 settles down by the gravity thereof. As a result, a pair electrode 31 is made to conduct to turn an input terminal of an inverter 34 of an angle of rotation generation circuit 24 to an L level and an output of the inverter 34 goes to an H level to beinto an arithmetic circuit 36. Thus, an angle of rotation the inserting section 8 being zero is outputted to the rotary processing circuit 25 as information signal and a signal not rotating is outputted to a TV monitor 6.