A rotator 2 is supported rotatably on a base 1, and a roller 7 is supported rotatably at the outer periphery of the rotator 2. A pressing member 4 has a circular arc pressing surface 4a and can be located selectively in a retracted position where a groove-shaped space 8 is formed between the pressing surface and the rotator and in a proximity position where the pressing surface is closer to the rotator. When the pressing member is in the retracted position, a pump tube can be inserted in the groove-shaped space. The pressing member is moved to the proximity position with the pump tube being held, and then the rotator is rotated, so that the pump tube is pressure-driven by the roller. The injection device with a simple structure easily can extract almost the entire semi-solidified nutritional supplement from a nutritional supplement container and inject it into a patient.
