To provide a multi-functional mask which is light weight and small in volume being easy to carry for the usual people, with built-in purification filter which can decompose and eliminate various harmful gas and fine dust which are harmful to the human body.

The multi-functional mask comprises a hood 1 comprising transparent films of thermosetting resin base, a structure 14 with an exhaust valve 22 attached to one face of the hood 1, a gas decomposing filter 11 and dust removing filters 9 and 12 closely connected with the structure 14, a structure 8 for air intake built-in with a dehumidifying filter 10, a structure 6 for sealing a front face composed of a silicone or a soft rubber material, a string adjusting member 7 for inserting a string 7 and adjusting for closely fixing the structure 6 for sealing the front face to a user's front face, and an adjusting string 5 for preventing various harmful gas and fine dust from coming in.