Abstract: A flow rate regulator includes a first cylindrical member, a second cylindrical member and a disc-shaped member to regulate, the flow rate of liquid flowing through a transfusion unit. The liquid is introduced into the second cylindrical member via an inlet port. It flows through the disc-shaped member via a through hole and flows further along a peripherally extending groove in the first cylindrical member. Then, it is discharged from the first cylindrical member via an outlet port after the flow rate is regulated as required. The disc-shaped member is fitted in the second cylindrical member so as not to be rotated relative to the latter, and the sub-assembly is then fitted into the first cylindrical member. The peripherally extending groove is so designed that its cross-sectional area is gradually varied on the bottom portion of the first cylindrical member. The through hole in the disc-shaped member is communicated with the peripherally extending groove.