A modular carrier for stair treads (15) is provided so that treads may be evenly spaced and hung between a pair of stringers (25, 25'). A pair of vertical side walls (16, 16') extend above the tread and have a mounting plate connected thereto lying in a plane which intersects the plane of the tread at a predetermined angle (.phi.). With the stringer set at this angle with respect to the horizontal, the treads lay in proper horizontal orientation. The plurality of notches or score lines are provided at the ends of the mounting plate (19, 20) which may be broken off, or overlapped, facilitating easy construction of evenly spaced stairs. Alternately, the left and right hand carriers are provided as separate units having a bottom plate 48 so that treads of varying widths may be used with the device.