An in-pipe robot that is carried into an existing pipe and can travel in the existing pipe, comprising: a chassis having on both sides side frames (42, 43) in which a horizontally extending slot (42a, 43a) is formed; a first wheel body to which pins (53, 54) slidable in the slot (42a, 43a) are attached on both sides and which is supported between the side frames (42, 43) via the pins (53, 54) and has traveling wheels (51, 52) attached to one end on both sides; a second wheel body that is supported between the side frames (42, 43) via pins (73, 74) attached on both sides on the same horizontal plane as the pins (53, 54) of the first wheel body and that has traveling wheels (71, 72) attached to one end on both sides, the other end on both sides being rotatably coupled to the other end of the first wheel body via axles (60, 63) to which intermediate wheels (62, 65) are attached, respectively; a rotary actuator mounted on the chassis such that the rotation axis thereof is on the same horizontal plane as the pins (53, 54, 73, 74) on both sides of the first and second wheel bodies (50, 70) and is located at the center between the traveling wheels (51, 52, 71, 72) of the first and second wheel bodies (50, 70); and elevating means (25, 55, 75) for sliding the pins (53, 54) of the first wheel body in the slots (42a, 43a) to rotate the first and second wheel bodies (50, 70) around the axles as a pivot and raise and lower the rotary actuator and the intermediate wheels (62, 65); wherein the intermediate wheels (62, 65) on both sides and the traveling wheels (51, 52, 71, 72) on both sides of the first and second wheel bodies (50, 70) all have the same shape and the wheel surfaces on each side have the same vertical plane, respectively; the pin (53, 54) on each side of the first wheel body is attached to the midpoint of a line connecting the traveling wheel center of the first wheel body and the intermediate wheel center on the same side, and the pin (73, 74) on each side of the second wheel body is attached to the midpoint of a line connecting the traveling wheel center of the second wheel body and the intermediate wheel center on the same side; and when the intermediate wheels (62, 65) on both sides are raised until they are brought into contact with the inner wall surface of the existing pipe by the elevating means (25, 55, 75), the radial distances to the rotation axis of the rotary actuator from points at which the traveling wheels (51, 52, 71, 72) on both sides of the first and second wheel bodies (50, 70) and the intermediate wheels (62, 65) on both sides come into contact with the inner wall surfaces of the existing pipe are respectively equal, and the rotation axis of the rotary actuator coincides with the pipe center axis of the existing pipe. a chassis having on both sides side frames (42, 43) in which a horizontally extending slot (42a, 43a) is formed; a first wheel body to which pins (53, 54) slidable in the slot (42a, 43a) are attached on both sides and which is supported between the side frames (42, 43) via the pins (53, 54) and has traveling wheels (51, 52) attached to one end on both sides; a second wheel body that is supported between the side frames (42, 43) via pins (73, 74) attached on both sides on the same horizontal plane as the pins (53, 54) of the first wheel body and that has traveling wheels (71, 72) attached to one end on both sides, the other end on both sides being rotatably coupled to the other end of the first wheel body via axles (60, 63) to which intermediate wheels (62, 65) are attached, respectively; a rotary actuator mounted on the chassis such that the rotation axis thereof is on the same horizontal plane as the pins (53, 54, 73, 74) on both sides of the first and second wheel bodies (50, 70) and is located at the center between the traveling wheels (51, 52, 71, 72) of the first and second wheel bodies (50, 70); and elevating means (25, 55, 75) for sliding the pins (53, 54) of the first wheel body in the slots (42a, 43a) to rotate the first and second wheel bodies (50, 70) around the axles as a pivot and raise and lower the rotary actuator and the intermediate wheels (62, 65); wherein the intermediate wheels (62, 65) on both sides and the traveling wheels (51, 52, 71, 72) on both sides of the first and second wheel bodies (50, 70) all have the same shape and the wheel surfaces on each side have the same vertical plane, respectively; the pin (53, 54) on each side of the first wheel body is attached to the midpoint of a line connecting the traveling wheel center of the first wheel body and the intermediate wheel center on the same side, and the pin (73, 74) on each side of the second wheel body is attached to the midpoint of a line connecting the traveling wheel center of the second wheel body and the intermediate wheel center on the same side; and when the intermediate wheels (62, 65) on both sides are raised until they are brought into contact with the inner wall surface of the existing pipe by the elevating means (25, 55, 75), the radial distances to the rotation axis of the rotary actuator from points at which the traveling wheels (51, 52, 71, 72) on both sides of the first and second wheel bodies (50, 70) and the intermediate wheels (62, 65) on both sides come into contact with the inner wall surfaces of the existing pipe are respectively equal, and the rotation axis of the rotary actuator coincides with the pipe center axis of the existing pipe.