To prevent a urine stored in a chamber pot from spilling out of the chamber pot during passing urine or when carrying the chamber pot after passing urine.

A device 10 for preventing a counter flow of stored urine, which is constituted from a cylinder member 11 for leading the urine and a valve 12 for preventing the counter flow, is detachably attached to a mouth 3 for receiving the urine of a chamber pot main body 1. The valve 12 for preventing the counter flow is formed from flat cylindrical films 14 which are formed from soft resin films, a pair of which surfaces are openably attached to each other and of which contacting surfaces are opened by an outer force and shut overlapped with each other at a normal state.