An igniter assembly having excellent moisture proof is provided. A cylindrical protruding portion 24 and a cylindrical stepped portion 25 are arranged in the metal collar 20. Shrinkage of a resin 30 after injection-molding produces a gap in an interface 50 but, to the contrary, in an interface 51, it presses the cylindrical stepped portion 25 and does not produce a gap. Thereby, since production of a continuous gap is prevented, entry of moisture is prevented.