A gas sensor composed of an oxygen ion conductive solid electrolyte, and formed by laminating a plurality of solid electrolyte layers on each of which a predetermined circuit pattern is formed, for specifying concentration of a predetermined gas component in a measurement gas on the basis of current flowing within said solid electrolyte by decomposing said predetermined gas component, said gas sensor comprising: an internal space (20, 40) to which the measurement gas is introduced; a reference gas space to which a reference gas is introduced; a plurality of pump electrodes (22, 23, 51) provided to face each of said internal space (20, 40) and an external space; a measuring electrode provided to face said internal space (20, 40); a reference electrode either provided to face said reference gas space or covered by a porous layer leading to said reference gas space; an oxygen partial pressure controlling pump cell (21, 50) composed of said plurality of pump electrodes (22, 23, 51) and said solid electrolyte existing among said plurality of pump electrodes, for pumping in and out oxygen between said internal space (20, 40) and said external space; a measuring pump cell composed of said measuring electrode, said reference electrode and said solid electrolyte existing therebetween, in which current flows in accordance with the amount of oxygen generated by decomposing said predetermined gas component within said internal space; a heater for electrically heating the proximity of said internal space (20, 40), which is provided between a first layer of said plurality of solid electrolyte layers and a second layer of said plurality of solid electrolyte layers, said second layer being laminated immediately above said first layer in the lamination order of said plurality of solid electrolyte layers; characterized by: two heater leads having substantially the same shape which are energizing paths to said heater and provided between said first layer and said second layer; a first lead for electrically connecting said reference electrode to outside; a second lead for electrically connecting said measuring electrode to outside; and a third lead for electrically connecting one of said plurality of pump electrodes (22, 23, 51) to outside; wherein said first lead is formed on said second layer of said plurality of layers, and arranged so as not to overlap any of said two heater leads as seen in the laminating direction of said first layer and second layer. an internal space (20, 40) to which the measurement gas is introduced; a reference gas space to which a reference gas is introduced; a plurality of pump electrodes (22, 23, 51) provided to face each of said internal space (20, 40) and an external space; a measuring electrode provided to face said internal space (20, 40); a reference electrode either provided to face said reference gas space or covered by a porous layer leading to said reference gas space; an oxygen partial pressure controlling pump cell (21, 50) composed of said plurality of pump electrodes (22, 23, 51) and said solid electrolyte existing among said plurality of pump electrodes, for pumping in and out oxygen between said internal space (20, 40) and said external space; a measuring pump cell composed of said measuring electrode, said reference electrode and said solid electrolyte existing therebetween, in which current flows in accordance with the amount of oxygen generated by decomposing said predetermined gas component within said internal space; a heater for electrically heating the proximity of said internal space (20, 40), which is provided between a first layer of said plurality of solid electrolyte layers and a second layer of said plurality of solid electrolyte layers, said second layer being laminated immediately above said first layer in the lamination order of said plurality of solid electrolyte layers; characterized by: two heater leads having substantially the same shape which are energizing paths to said heater and provided between said first layer and said second layer; a first lead for electrically connecting said reference electrode to outside; a second lead for electrically connecting said measuring electrode to outside; and a third lead for electrically connecting one of said plurality of pump electrodes (22, 23, 51) to outside; wherein said first lead is formed on said second layer of said plurality of layers, and arranged so as not to overlap any of said two heater leads as seen in the laminating direction of said first layer and second layer. two heater leads having substantially the same shape which are energizing paths to said heater and provided between said first layer and said second layer; a first lead for electrically connecting said reference electrode to outside; a second lead for electrically connecting said measuring electrode to outside; and a third lead for electrically connecting one of said plurality of pump electrodes (22, 23, 51) to outside; wherein said first lead is formed on said second layer of said plurality of layers, and arranged so as not to overlap any of said two heater leads as seen in the laminating direction of said first layer and second layer.