An oxygen sensor for detecting gas concentration based on either an electric current value or a resistance value measured when a voltage is applied to a sensor element includes gaps formed between electrodes arranged in an element main body and ridges where surfaces of an element touch each other. These gaps will be escaping parts for expansion and contraction of electrode material that accompany thermal expansion and contraction of a sensor main body, and concentration of thermal stress at edge parts of the element main body may thus be eliminated, thereby alleviating thermal stress on the oxygen sensor. This allows provision of a gas sensor that controls generation of cracks in the element and that is stably usable over a long period of time.