A gas sensor includes a structural body made from an oxygen ion conductive solid electrolyte, a gas introduction passage which is formed in the structural body and into which a gas to be measured is introduced, a main adjustment chamber that communicates with the gas introduction passage, and a measurement chamber that communicates with the main adjustment chamber. A buffer space that communicates with the gas introduction passage, and at least two diffusion rate control members that communicate with the buffer space, are provided between the gas introduction passage and the main adjustment chamber. The respective widths Wb1 and Wb2 of the diffusion rate control members are less than the respective widths Wa, Wc, and Wd of the gas introduction passage, the buffer space, and the main adjustment chamber.