A pharmaceutical cartridge holding unit (2) holds a pharmaceutical cartridge (5) and is mounted to a pharmaceutical injection device main body (100) in order to mount the pharmaceutical cartridge (5) to a pharmaceutical injection device. The pharmaceutical cartridge holding unit (2) comprises an outer peripheral cap (3) having a distal end opening (3f) and a rear end opening (3e), and a cartridge cover (4) that is disposed on the inside of the outer peripheral cap (3) and is held in a state of being able to slide forward and backward with respect to the outer peripheral cap (3). The outer peripheral cap (3) has a guide component (9) that guides the sliding of the cartridge cover (4) forward and backward, stoppers (30a, 30b) that prevent the cartridge cover (4) from coming loose from the outer peripheral cap (3), and protrusions (3b) that can engage with the pharmaceutical injection device main body (100).
