To realize smooth urine sampling by securely preventing leak of urine to the external, and achieving smooth air ventilation.

In composing an air vent valve 1 for a liquid containing bag 2 to discharge inner air A in the liquid containing bag 2 to the external by providing it in the liquid containing bag 2 that is sealed, a small hole part (outer side small hole part) 3 is provided at an upper part of the liquid containing bag A, and a valve body part 4 having permeability which becomes impermeable to water by absorbing water is provided on the outer side small hole part 3.