It is intended to make the injection of a drug liquid more appropriate depending ON the physical conditions of a subject. A liquid drug injection device (100) which has an injection-controlling unit (103) and an injection head (110) for operating a liquid drug syringe for injecting a liquid drug into a subject. The injection-controlling unit (103) comprises an operation panel (104) into which the physical data of the subject and so ON are input and a lean body weight computing section (107) whereby the lean body weight is computed based ON the physical data input above and an injection condition-determining section (197) whereby the injection conditions of a liquid drug are determined based ON the lean body weight calculated above and a controlling section (109) whereby the operation of the liquid drug syringe is controlled so that the liquid drug is injected in accordance with the injection conditions determined above.
