PURPOSE: To facilitate the assaying of blood components, by making a calibration solution in a calibration substance solution storage tank flow into a cylinder through a check valve so a to further inject a solution in the cylinder into a carrier liquid passage.

CONSTITUTION: A first tank 81 storing a substance L1 to be inspected (e.g. glucose) alone and a second tank 82 storing an inteference substance L2 are provided to calibrate a blood component assay apparatus. First, a piston 3a of a cylinder 3 is pulled up to run a glucose solution L1 into the cylinder chamber through a check valve 2a and then, it 3a is pushed down to run the glucose solution L1 into a carrier liquid passage 36 through a check valve 2b. After a specified time, a piston 5a of a cylinder 5 is operated to make the interference substance flow into the carrier liquid passage 36 likewise. After this operation, a blood sample sampled is injected into the carrier liquid passage 36 and correction is made based on a detection signal with the inflow of a calibration substance to assay substance to be inspected.