Endoscopic therapeutic device and double tube for therapeutic device

An endoscopic therapeutic device comprising:

• a double tube configured to be inserted through a channel of an endoscope, wherein the double tube includes:
• a flexible outer tube;
• and
• a flexible inner tube inserted through the outer tube and configured to be advanced and retracted relative to the outer tube,
• wherein in the double tube,
• the inner tube and the outer tube are made of different types of plastic materials such that an affinity between an outer circumferential sliding contact surface of the inner tube, and an inner circumferential sliding contact surface of the outer tube is reduced, as compared to where the inner tube and outer tube are made of a same type of plastic material, and a frictional resistance between the sliding contact surfaces is lowered when the inner tube and the outer tube are relatively advanced or retracted while the double tube is curved to follow a pathway of the channel, and
• the outer tube is made of a material more rigid than that of the inner tube such that crushing of the outer tube at a bent position of the double tube which follows the pathway of the channel is prevented and an increase in the frictional resistance between the sliding contact surfaces when the inner tube and the outer tube are relatively advanced or retracted is prevented.