A pair of side pads, which are arranged to face each other by having a negative pressure generating part in the direction orthogonal to an air flow direction of a slider therebetween, are made to have three or more steps, respectively. Of the respective surfaces having the plural steps, the surfaces having a highest height respectively are not subject to a milling, and the respective surfaces of having plural steps are made to gradually have a deeper cavity depth as the surface comes closer to the air inflow end. Further, it is also effective for improving the efficiency in positive pressure generation to surround the second side pad region partially by the region of the surface being not subject to the milling, and to surround the third side pad region partially by the second surface region.