This endoscope treatment instrument is provided with a sheath which is configured to be insertable into a channel of the endoscope, a treatment unit which is disposed at the leading end of the sheath, an elongate member which is inserted into the sheath so as to allow advancing and retracting, connects at the leading end to the treatment unit, and operates the treatment unit by advancing and retracting with respect to the sheath, and an operation unit which is provided on the base end of the sheath. The operation unit comprises an operation unit main body connected to the sheath, a slider provided movably along the axial direction of the sheath with respect to the operation unit main body and connected to the base end of the elongate member, and a constant load spring provided on the operation unit main body and biasing the slider towards the base end with a constant force regardless of the position of the slider.
