Sensor element and gas sensor including the same

A sensor element comprising:

• plate-shaped portions that include a first portion, a second portion, and a third portion, wherein
• the plate-shaped portions extend in a direction of an axial line and are stacked in a stacking direction intersecting the direction of the axial line, the first portion includes a solid electrolyte body, a reference gas-side electrode and a measurement gas-side electrode which is disposed on surfaces of the solid electrolyte body,
• the second portion has a reference gas introduction hole to which the reference gas-side electrode is exposed and which is open toward a rear end side in the direction of the axial line,
• the third portion includes a heat generating portion and a pair of lead portions, the heat generating portion including a pair of outer linear portions, a pair of inner linear portions disposed between the outer linear portions, first connection portions each of which connects together forward ends of the outer linear portion and the inner linear portion located adjacent to each other, and a second connection portion which connects together rear ends of the pair of inner linear portions, the pair of lead portions being connected to rear ends of the respective outer linear portions,
• in a cross section of the sensor element, which cross section includes the heat generating portion and is perpendicular to the direction of the axial line, the pair of inner linear portions are disposed so as not to overlap the reference gas introduction hole in the stacking direction, and
• a relation L3<L4 is satisfied, where L3 is a length between each of the outer linear portions and an adjacent one of the inner linear portions, and L4 is a length between the pair of inner linear portions adjacent to each other.