At least an inner tube and an outer tube of a double tube, which forms an insertion section of an endoscopic injector, are formed of different kinds of plastic materials, and the outer tube is formed of a material with a higher rigidity than a material of the inner tube. Thereby, there are provided an endoscopic therapeutic device such as an endoscopic injector, and a double tube for a therapeutic device, which have a good operability of, for example, an operation of projecting a needle, and can perform a stable operation for a diseased part.