Device closely contacting object surface and movable

A device capable of adhering to and moving along a surface of an object immersed in liquid, comprising:

• a main casing at least comprising an outer casing and an inner casing;
• an outer sealing member mounted at an opening of the outer casing, part of which is caused to contact the surface of the object;
• an inner sealing member mounted at an opening of the inner casing, part of which is caused to contact the surface of the object;
• and
• a first means for moving along the surface of the object while maintaining a certain distance between the main casing and the surface of the object;
• wherein at least the outer casing, the outer sealing member and the inner sealing member, together with the surface of the object, define Area I, and at least the inner casing and the inner sealing member, together with the surface of the object, define Area II;
• wherein the main casing is configured so that a pressure of fluid in Area I is maintained at a lower level than a pressure of fluid surrounding the Device, and a pressure of fluid in Area II is maintained at a higher level than the pressure of fluid in Area I.