Fuel tank ventilation valve for internal combustion engines

In a vent valve structure including a cut valve (20) that shuts off the flow of fuel vapor and fuel liquid, a positive pressure adjustment valve (30) that opens when positive pressure is applied, and a negative pressure adjustment valve (40) that opens when negative pressure is applied, the negative pressure adjustment valve (40) is provided in a row arrangement with the cut valve (20) in a position linking a ventilating passage (6) and a fuel tank (2) so as to bypass the valve opening (22a) of the cut valve (20).