A hot iron such as a soldering iron, a plastic welding machine, iron, hair iron, and others, which is used while a workpiece is being observed, particularly those which can be used several seconds after a switch is turned on, wherein a hot iron is formed by thinning a metal plate made of an iron chromium alloy as a heater wire (3) to a limit at which the shape of that metal can be maintained, forming an electrical insulation body (2) with a thin plate such as an aluminum nitride which is approx. 10 times higher in thermal conductivity than the heater wire (3), using, as an iron tip heat storing part (1), a steel which is 2 times or more higher in thermal conductivity and which is larger in thermal capacity than the electrical insulation body (2), and sticking them closely to each other by pressing them with a heat insulated supporting device; a method of controlling the hot iron such as a soldering iron, comprising the steps of feeding a large set power to the heater wire (3) for a set short time every time switches (4, 7) are operated so as to raise the temperature of the iron tip heat storing part (1) rapidly so that a desired temperature can be obtained by several simple operations of the switches (4, 7).