We propose a multicast-buffer ATM switch, where a dedicated buffer is allocated to store all multicast cells in an ATM switch. We describe the design of the dedicated multicast buffer in an output-buffer ATM switch and in a shared-buffer ATM switch. No additional copy circuit or complicated control circuit is needed to implement the multicast-buffer ATM switch. Our performance evaluation shows that the proposed switch has a low cell-loss ratio. We are implementing an eight-by-eight output buffer ATM switch with the multicast buffer. We also present a window control mechanism to further improve the utilization of the multicast buffer. Therefore, we believe the multicast-buffer ATM switch is a good candidate to support the multicast function for future broadband ISDN applications