To provide a liquid injection apparatus embedded in a human body to be used with which the remaining amount of a liquid to be injected into the body such as chemicals can be correctly measured to prevent shortage of the liquid.

The apparatus has a main body 2 capable of being embedded into the body and consisting of a highly rigid air-tight container, a liquid tank 3 provided in the main body and made of a soft material, a pump 7 for injecting the liquid stored in the tank into the human body, pressure sensors 8 and 9 provided in the main body, and a liquid remaining amount detecting section 5 for determining the remaining amount of the liquid in the tank on the basis of a pressure value detected by the pressure sensors.