Oxygen sensor

An oxygen sensor (1) comprising: an oxygen sensing element (2) shaped like a hollow shaft with a tip closed; a shaft-like heating element (3) being placed in the hollow part of said oxygen sensing element (2) for heating said oxygen sensing element (2); a cylindrical casing (10) for housing said oxygen sensing element (2); and a ceramic seperator (18) being placed almost coaxially with a rear end of said oxygen sensing element (2) and formed with a plurality of lead insertion holes (72) axially penetrating said ceramic separator (18) for inserting leads (20, 21, 28, 29) from said oxygen sensing element (2) and said heating element (3); wherein the lead insertion holes (72) are arranged so as to surround a center axis of said ceramic separator (18); said ceramic separator (18) is formed with a heating element end housing hole (102) opened at one end in the front end face of said ceramic separator (18) with a bottom positioned in an axial intermediate part of said ceramic separator (18) and an inner diameter set larger than an outer diameter of said heating element (3), the heating element end housing hole (102) being formed by cutting away a center of said ceramic seperator (18) so as to overlap the separator lead insertion holes (72) from the inside and the rear end part of said heating element (3) being housed in the heating element end housing hole; and said heating element (3) is offset so that a center axis thereof is one-sided with respect to a center axis of the hollow part of said oxygen sensing element (2) in the proximity of a heating part of said heating element (3).