A contrast liquid injector has a controller that calculates a necessary volume of the contrast medium based on a read out necessary dose of effective component per unit weight, weight of the subject, and concentration of the effective component. The injection rate of a base-operation condition is changed based on the calculated necessary volume of the contrast medium, wherein the predetermined injection time is unchanged, for all volumes of the contrast medium, when making the injection pattern, whereby a timing of an optimum concentration of the contrast medium will be substantially unchanged for all volumes of the contrast medium.