A puncture assistance system provides information on a collapse state of a blood vessel to be punctured, caused by pressing action of an ultrasonic probe, when ultrasonic images of the blood vessel are acquired. A puncture assistance system 10 includes: vascular diameter detecting means 18 for detecting a vascular diameter during acquisition of the ultrasonic images from an ultrasonic diagnostic device 11 puncture assistance information generating means 12 for generating puncture assistance information for determination of whether or not puncture is allowed to be performed based on a collapse state of a blood vessel B caused by pressing action of an ultrasonic probe 15 against skin S by comparing a current vascular diameter detected by the vascular diameter detecting means 18 with a standard vascular diameter stored in advance and a monitor 19 that presents the puncture assistance information.