A liquid injector for injecting at least a contrast medium into a subject whose fluoroscopic image is to be captured by an imaging diagnostic apparatus, the liquid injector is configured to connect with the imaging diagnostic apparatus, wherein said contrast medium is available in a plurality of types having different concentrations of an effective component, said liquid injector comprising: an injection head having a piston actuating mechanism, for injecting at least said contrast medium into said subject; and a controller unit for controlling operation of said piston actuating mechanism under an operating-condition, having a display and touch panel; said display and touch panel being adapted to display a plurality of body sections in schematic images of human body shape; wherein when one of the body section is selected, said display and touch panel is further adapted to display at least one region to be imaged of the human body in schematic image; and said controller unit is adapted to perform: (i) reading out from condition storage means a base operation-condition including a predetermined injection time for the selected region to be imaged, and a necessary dose of effective component of the contrast medium per unit weight of the subject, (ii) calculating a total amount of the contrast medium to be injected, based on the read out necessary dose of effective component per unit weight, concentration of the effective component, and subject's weight as a body item, (iii) making an injection-pattern as the operation-condition based on the total amount of contrast medium and the base operation-condition, wherein the injection rate of said base operation-condition is modified in accordance with the total amount of the contrast medium while the injection time is not changed, (iv) performing injection of said contrast medium based on said injection-pattern by controlling the operation of the piston actuating mechanism. an injection head having a piston actuating mechanism, for injecting at least said contrast medium into said subject; and a controller unit for controlling operation of said piston actuating mechanism under an operating-condition, having a display and touch panel; said display and touch panel being adapted to display a plurality of body sections in schematic images of human body shape; wherein when one of the body section is selected, said display and touch panel is further adapted to display at least one region to be imaged of the human body in schematic image; and said controller unit is adapted to perform: (i) reading out from condition storage means a base operation-condition including a predetermined injection time for the selected region to be imaged, and a necessary dose of effective component of the contrast medium per unit weight of the subject, (ii) calculating a total amount of the contrast medium to be injected, based on the read out necessary dose of effective component per unit weight, concentration of the effective component, and subject's weight as a body item, (iii) making an injection-pattern as the operation-condition based on the total amount of contrast medium and the base operation-condition, wherein the injection rate of said base operation-condition is modified in accordance with the total amount of the contrast medium while the injection time is not changed, (iv) performing injection of said contrast medium based on said injection-pattern by controlling the operation of the piston actuating mechanism. (i) reading out from condition storage means a base operation-condition including a predetermined injection time for the selected region to be imaged, and a necessary dose of effective component of the contrast medium per unit weight of the subject, (ii) calculating a total amount of the contrast medium to be injected, based on the read out necessary dose of effective component per unit weight, concentration of the effective component, and subject's weight as a body item, (iii) making an injection-pattern as the operation-condition based on the total amount of contrast medium and the base operation-condition, wherein the injection rate of said base operation-condition is modified in accordance with the total amount of the contrast medium while the injection time is not changed, (iv) performing injection of said contrast medium based on said injection-pattern by controlling the operation of the piston actuating mechanism.