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.