To smoothly introduce urine, to prevent leaking of urine and odors and to prevent intrusion and release of bacteria and the like to prevent infections.

A urine collection bag 1 has a bag-shaped urine storage part 11 comprising a front sheet 1f and a back sheet 10b fused to each other, and allows introduced urine Ur to flow into the urine storage part 11 from an urine introducing tube T and an inflow part 3 to collect it. When the urine Ur flows in, a backflow preventing part 31 opens a valve element part to permit inflow of the urine Ur; when the internal pressure of the urine storage part 11 has built up, the backflow preventing part 31 closes the valve element part to prevent backflow of the urine Ur to prevent infections via the urinary tract. When the internal pressure has built up, an internal gas is passed from a ventilating part through an antibacterial agent and a deodorant contained in the porous resin molding of a ventilating element, to kill bacteria and remove odors. Particles of a water-absorptive polymer compound are dispersed in the ventilating part, and the particles swell on intrusion of the urine Ur and regulate passage through the ventilating part to prevent infections.