A guide assembly for an endoscope has an elongated tube for entry in a body cavity. Plural endless belts move in an axial direction of the elongated tube in contact with a cavity wall of the body cavity, to propel the elongated tube. A driving device is engaged with a first belt surface of the belts, for rotating to drive the belts. A pressure roller has a smaller width than a width of the belts in a transverse direction crosswise to the axial direction, for pressing the belts by contacting a second belt surface reverse to the first belt surface, to apply tension thereto together with the driving device. A regulating projection is formed to project from the second belt surface and to extend in the axial direction, for contacting a side surface of the pressure roller in the transverse direction, to prevent lateral misalignment of the belts.
