An endoscope for treatment suitable to the treatment in a body cavity comprises an elongated soft observing optical unit having at least an observing optical system; and a unit inserting tool having a unit inserting channel in which the observing optical unit is inserted and a treatment tool inserting channel in which a treatment tool is inserted. The unit inserting channel of the unit inserting tool has a branching portion at which the unit inserting channel is branched into a first inserting channel and a second inserting channel. An observing window which is arranged at the end opening of the first inserting channel is provided in a surface at the distal-end and an observing window which is arranged at the end opening of the second inserting channel is provided in a surface at the halfway portion. The unit inserting tool comprises an optical unit guiding port for guiding the observing optical unit and at least one treatment tool lead-in port in which a treatment tool is inserted at the proximal end portion and a treatment tool lead-out port which is communicated with the treatment tool inserting channel that extends from the treatment tool lead-in port at least in one of the surface at the distal-end and the surface at the halfway portion.