PURPOSE: To restrain transmission of gas flow sound from an evaporated fuel purge piping system having a duty control changeover valve and damp a pulsating sound.

CONSTITUTION: Respective middle parts of the inlet side passage and the outlet side passage of a duty control changeover valve 33 are constituted of metallic pipes 31, 35, and they are fixed on the engine side through a bracket 30. A hose of the part apt to be a problem concerning transmission of sound is constituted out of a rubber hose containing braids. For damping pulsation, the diameter of the inlet side passage of the changeover valve is fundamentally enlarged, and it is steppedly restricted with approaching the changeover valve 33.