An endoscope is provided with a sheath which is removably fitted over an insert tube to isolate it from the external environment. A plurality of channels are provided for passing fluids, each channel having an opening at one end near the distal end portion of the sheath and extending at the other end past the proximal end of the sheath. A channel connecting device is provided at the extending end portions of the channels. The channel connecting device is capable of simultaneously and detachably connecting at least two of the channels to respective channels in the endoscope through respective connecting conduits, which are provided in a control part of the endoscope. Respective end portions of the channels are disposed in substantially parallel relations to each other, and the connecting conduits are disposed in a direction which is perpendicular to the axes of the end portions of the channels. In addition, a packing is provided in an opening at the proximal end of the sheath which is movable in the radial direction of the sheath to enable the insert tube to be inserted into and removed from the sheath while the outer peripheral surface of the insert tube remains hermetically sealed.