A heater according to an embodiment of the present disclosure includes a heater element including a flat heat generating body, a linear slit formed in a linearly opened manner with one end arranged at an outer circumference of the heat generating body and the other end arranged in the turnover portion of the heat generating body, and a turnover portion formed in an opened manner to continue from the other end, an opening diameter of the turnover portion being larger than a slit width of the linear slit, the heater element generating heat by electrification, and a pair of electrodes connected to a predetermined face of the heater element, a voltage being applied on the electrodes during electrification of the heater element.