A liquid injector acquires personal condition data originating from a patient, before executing injection of a medical liquid, and a function decision unit decides whether the patient has renal dysfunction based on the acquired personal condition data. Accordingly, such arrangement can be made that in the case where the patient is not decided to have renal dysfunction the liquid injection is executed without announcing an alert, and that in the contrary case the alert is announced and the liquid injection is suspended. Thus, the liquid injector allows easily and surely preventing improper injection of the liquid such as a contrast medium to a patient with renal dysfunction.