Sensor element and gas sensor

A gas sensor element comprising:

• an element body having an oxygen-ion-conductive solid electrolyte layer and provided with a measurement-object gas flow section therein, the measurement-object gas flow section introducing a measurement-object gas and causing the measurement-object gas to flow therethrough;
• a reference electrode disposed inside the element body;
• and
• a reference-gas introduction section that is disposed inside the element body, and causes a reference gas to flow to the reference electrode, the reference gas serving as a reference for detecting a specific gas concentration in the measurement-object gas,
• wherein the reference-gas introduction section has a reference-gas flow path, and one or more preliminary chambers which are disposed in a middle of the reference-gas flow path, and have a diffusion resistance lower than a diffusion resistance of the reference-gas flow path, and
• at least part of the reference-gas flow path is composed of a porous body wherein the reference gas from an outside of the element body flows through the porous body to any of the one or more preliminary chambers.