A hanging device (100A) used in method for transferring an additive solution includes an upper hanging section (106) and a support mechanism (lower hanging section (108)). The upper hanging section (106) is used to hang a medical fluid bag (54) upside down. The support mechanism (lower hanging section (108)) supports a primary bag (50) or a transfer line (55) in a predetermined state such that, when a red blood cell preservation (M) is transferred from the medical fluid bag (54) to the primary bag (50) using the height difference between the primary bag (50) and the medical fluid bag (54), air from the medical fluid bag (54) is stopped in the middle of the transfer line (55).
