A
limiting current type gas sensor (100) capable of indicating a
NOx concentration in a measurement gas, comprising: a sensor element (101) formed from an
oxygen ion-conducting
solid electrolyte (1, 2, 3, 4, 5, 6), the sensor element (101) comprising: a gas inlet (10) into which a measuring gas is introduced from the outside; a first
interior space (20) connected to the gas inlet (10) at a predetermined
diffusion resistance; a second
interior space (40) connected to the first
interior space (20) at a predetermined
diffusion resistance; a main pumping
cell (21) which is an electrochemical pumping
cell consisting of an inner pumping
electrode (22) facing the first inner space (20), an outer pumping
electrode (23) provided on a surface of the sensor element (101), and the
solid electrolyte (4, 5, 6) located between the inner pumping
electrode (22) and the outer pumping electrode (23); a measuring electrode (44) facing the second inner space (40) and covered with a porous protective film (45) providing a predetermined
diffusion resistance, the measuring electrode (44) serving as a reduction catalyst for
NOx; an
atmospheric air introduction layer (48) into which
atmospheric air is introduced from outside the sensor element (101) as a reference gas; a
reference electrode (42) covered with the
atmospheric air introduction layer (48); and a measuring pump
cell (41), which is an electrochemical pump cell consisting of the measuring electrode (44), the outer pump electrode (23) and the
solid electrolyte (4, 5, 6) located between the measuring electrode (44) and the outer pump electrode (23); and a concentration specifying element (110) that specifies a concentration of
NOx based on a magnitude of a NOx current (Ip2) flowing between the measuring electrode (44) and the outer pumping electrode (23) in the measuring pumping cell (41), wherein the main pumping cell (21) is configured and arranged to pump out
oxygen in the first internal space (20) when a predetermined main pumping
voltage (Vp0) is applied between the inner pumping electrode (22) and the outer pumping electrode (23), and pumps out
oxygen in the measurement gas introduced to the first internal space (20) to lower the oxygen
partial pressure of the measurement gas in the first internal space (20), the measuring pumping cell (41) is configured and arranged to pump out oxygen in the vicinity of the measuring electrode (44) when a predetermined pumping
voltage (Vp0) is applied between the inner pumping electrode (22) and the outer pumping electrode (23), and to pump out oxygen generated by a reduction of NOx in the measuring gas that reaches the vicinity of the measuring electrode (44) at the measuring electrode (44), a
diffusion resistance from the gas inlet (10) to the inner pump electrode (22) equal to or greater than 200 cm -1 and equal to or less than 1000 cm -1 an electrical resistance of the main pump cell (21) is equal to or less than 150Ω, and a
shortest distance from the inner pump electrode (22) to the outer pump electrode (23) is equal to or greater than 0.1 mm and equal to or less than 0.6 mm and the inner pumping electrode (22) is a
cermet electrode made of an Au-Pt
alloy and ZrO2 with an area equal to or greater than 5 mm 2 and equal to or less than 20 mm 2 is formed.