A gas sensor comprises a gas sensing element, a housing for the gas sensing element, and an element cover secured to an axial end of the housing and composed of an inner cover covering part of the gas sensing element and an outer cover disposed outside the inner cover. The outer cover comprise an approximately cylindrical side wall body, a bottom body integral with the side wall body, and a guide having first and second ends, the first end being secured to the side wall body and the second end being separated from the side wall body and located to provide a side opening between the second end and the side wall body. The side opening introduces a gas thereinto. A discharge opening is formed through the bottom body. The second end is recessed inward in the outer cover and is closer to the bottom body than the first end.