function emptyMC(mc) {
    this.no = ++_global.mcCount;
    this.mc = mc.createEmptyMovieClip("newMC"+this.no, this.no);
    this.mc.setMask(mc.maskMC); //<-----追加
}

function makeTicker() {
     mcObj1 = new emptyMC(this); //<------変更
    fldObjProps = {mc:mcObj1.mc, x:Stage.width, y:180, speed:100};
    fldStyleProps = {background:false};
    .....//以下同じ
}