A steam iron, comprising a lower plate (3) with steam supply holes (4) and at least a first conduit (2) of steam flow to said plate (3); the supply of steam into said first conduit (2) being controlled by a button (5) controlling the steam production means housed in the iron or in an external machine body thereof; said iron comprising a second conduit (2a) which branches from said first conduit (2) to carry the steam to at least one outflow hole (14) from at least one side of the box-shaped body (1) of the iron, for example the front side (101); downstream of the branch-point of said first and second conduits (2, 2a) and in one of said first and second conduits (2, 2a), opening and closing means (8, 21, 31) of the first conduit (2) are positioned, controllable from the outside and allowing or not allowing the steam flow into it; in the second conduit (2a), a valve with a duly calibrated valve shutter (18) being positioned and opening automatically, thanks to the pressure of the steam flowing into said second conduit (2a), when said means (8, 21, 31) close the relative first conduit (2), and closing automatically when said means (8, 21, 31) open the relative first conduit (2) and channel the steam into it.