Gas sensor

A gas sensor comprising:

• a sensor element having a gas inlet through which measurement-object gas is introduced and capable of detecting a concentration of a predetermined gas in the measurement-object gas that flows into the sensor element through the gas inlet;
• an inner protective cover that has a sensor element chamber thereinside and in which one or more element-chamber inlet and one or more element-chamber outlet are arranged, the sensor element chamber accommodating a front end of the sensor element and the gas inlet, the element-chamber inlet being an entrance to the sensor element chamber, and the element-chamber outlet being an exit from the sensor element chamber;
• and
• an outer protective cover that is disposed outside the inner protective cover and in which one or more outer inlet and one or more outer outlet are arranged, the outer inlet being an entrance from outside for the measurement-object gas, and the outer outlet being an exit to the outside for the measurement-object gas,
• wherein the outer protective cover and the inner protective cover form a first gas chamber and a second gas chamber as spaces therebetween, the first gas chamber being at least a portion of a flow channel for the measurement-object gas between the outer inlet and the element-chamber inlet, and the second gas chamber being at least a portion of a flow channel for the measurement-object gas between the outer outlet and the element-chamber outlet and not being directly connected to the first gas chamber, and
• a cross-sectional area ratio S1/S2, which is a ratio of a total cross-sectional area S1 [mm2] of the outer inlet to a total cross-sectional area S2 [mm2] of the outer outlet, is more than 2.0 and 5.0 or less.