A machining head replaceable rotating tool having a fastening male screw and a fastening female screw disposed on respective shaft centers of one and the other of a machining head and a holder, the fastening male and female screws being threadably engaged with each other to concentrically and removably attach the machining head to a tip portion of the holder, the machining head and the holder being disposed with abutting surfaces abutted against each other in a fastened state when the fastening male and female screws are threadably engaged, the machining head replaceable rotating tool being integrally and rotationally driven via the holder in a tool rotation direction causing the fastening male and female screws to be fastened by a machining load to perform predetermined machining with the machining head, the abutment of the abutting surfaces preventing the fastening male and female screws from being further fastened by a machining load, the fastening male and female screws being saw-tooth buttress screws having a following flank angle α smaller than a leading flank angle β.