A heater includes: a ceramic body having a rod-like shape; and a heat generating resistor embedded in the ceramic body, the heat generating resistor including a first straight line section, a second straight line section which is disposed alongside the first straight line section, and a folded section which connects the first straight line section and the second straight line section, in a transverse cross section of the heater, the first straight line section having a shape having a first major axis, the second straight line section having a shape having a second major axis, the second major axis being inclined with respect to the first major axis, a centroid of the first straight line section and the second straight line section being deviated from a centroid of the ceramic body to a side on which a distance between the first major axis and the second major axis is narrower.