The priming method includes the steps of: in a state where a contrast agent bag (16) containing a contrast agent (Z) is coupled to a second tube (10B), moving a second piston (512B) in a second syringe (510B) backward to introduce the contrast agent to the second syringe (510B), and with a first tube (10A) kept open, moving the second piston (511 B) in the second syringe (510B) forward to discharge air in the second syringe (510B) to the outside and to fill the first tube (10A) with contrast agent (Z).
