SYRINGE CAP ASSEMBLY

A syringe cap assembly (10) to be attached to an ejection port at a proximal end of a syringe (11) includes: a lock collar (13) to be attached to the ejection port at the proximal end of the syringe (11); and a plastic cap (14) screwed and thereby tightened into the lock collar (13). An external surface of the lock collar (13) has a plurality of projecting ribs (13a) that are each extended in an axial direction and are arranged in a circumferential direction to define a plurality of recessed grooves (13b) that are each extended in the axial direction and located between adjacent projecting ribs (13a) of the plurality of projecting ribs (13a) that are adjacent to each other in the circumferential direction. A bottom of an external surface of the plastic cap (14) includes a protrusion (14p) extending in a direction toward the lock collar (13). At a stage where tightening rotation of the plastic cap (14) implemented by screwing the plastic cap (14) into the lock collar (13) is completed, the protrusion (14p) is located in the recessed groove (13b) between the adjacent projecting ribs (13a).