Patent ID: 7870777

Claim:
A gas sensor having an axis comprising: a detecting element extending in an axial direction of the gas sensor, and having a detecting portion for detecting a gas to be detected on a leading end side of the detecting element; a metal shell surrounding a radial periphery of the detecting element such that the detecting portion protrudes from a leading end of the metal shell; an outer cylinder that is fixed to the metal shell, and which surrounds the radial periphery of a rear end portion of the detecting element; and a plug member provided in a rear end of the outer cylinder, the plug member including a lead wire insertion hole through which a lead wire is inserted, and an air vent provided with a filter member having air permeability and waterproofness, wherein the gas sensor comprises a first protective member that covers the air vent of the plug member so as to protect the filter member, the first protective member having a ventilation portion having an opening smaller than an opening of the air vent and at least partially overlapping the air vent in the axial direction, and at least one of the outer cylinder and the plug member is provided with a locking portion that limits rotation of the first protective member around the axis.