To provide a push-assist device allowing a simple injecting operation without using a special device when injecting a viscous nutrient or semisolid nutrient into a patient's body and discharging the nutrient with scarcely leaving undischarged nutrient in a container.

The push-assist device is provided with a buffer fluid body sealed with buffer fluid object in its lumen, and a pushing means for pushing a storage container storing another fluid object to be let out (discharged) via the buffer fluid body; and the buffer fluid body covers the substantial outer face whole body of the storage container.