Herein disclosed is a ply-band building apparatus which generally includes a main rotary shaft journaled on a fixed base, a ply-band building drum constituted by a plurality of arcuate segments collectively defining the drum surface thereof and a mechanism mounting the arcuate segments on the rotary shaft in such a manner as to permit the arcuate segments simultaneously and radially move thereby to vary the diameter of the drum surface, and drum diameter control means engaged with the mechanism for actuating the mechanism so as to permit the plyband building drum to be in one of a maximum expanded state, an intermediate operable state and a minimum retracted state.