Patent ID: 8506780

Claim:
A gas sensor which has a sensor element constituted by an oxygen-ion conductive solid electrolyte as a main component and detects a predetermined gas component in a measurement gas, said sensor element comprising: an internal space to which the measurement gas is introduced from the outside; a diffusion control part in communication with said internal space in a lengthwise direction of said sensor element, said diffusion control part forming a slit-like space with a smaller thickness than that of said internal space, said diffusion control part applying a predetermined diffusion resistance to the measurement gas having been introduced to said internal space; a pumping cell that pumps out oxygen existing in said internal space; and a measuring cell, said pumping cell comprising: a first electrode formed on a surface of said internal space; and a second electrode formed in a space different from said internal space, said pumping cell pumping out oxygen existing in said internal space when a predetermined voltage is applied between said first electrode and said second electrode, said measuring cell comprising: a third electrode formed in said diffusion control part, said third electrode reducing an oxide gas component in said predetermined gas component to which said predetermined diffusion resistance has been applied by said diffusion control part; and a fourth electrode formed in a part different from said diffusion control part, said measuring cell measuring a current flowing between said third electrode and said fourth electrode when a voltage is applied between said third electrode and said fourth electrode, wherein a cross-sectional opening area of a part where said diffusion control part and said internal space communicate with each other is 0.005 mm 2 or more and 0.3 mm 2 or less, and a distance from a boundary between said diffusion control part and said internal space to an end of said third electrode at a side opposite to said internal space is 0.3 mm or more 2.0 mm or less.