A syringe holding structure includes an adapter case (40) for holding a small-diameter syringe, and a syringe holding member having a flange-receiving groove (77) for holing flange portion (46) of the case(40). The syringe holding structure further includes locking mechanism for fixing the flange portion (46) in the groove (77) when the flange portion is inserted into flange-receiving groove and then it is rotated by 90 degrees about its axis.
