An algorithm for clock scheduling of concurrent-flow clocking rapid single-flux-quantum (RSFQ) digital circuits is proposed. RSFQ circuit technology is an emerging technology of digital circuits. In concurrent-flow clocking RSFQ digital circuits, all logic gates are driven by clock pulses. Appropriate clock scheduling makes clock frequency of the circuits higher. Given a clock period, the proposed algorithm determines the arrival time of clock pulses and the delay that should be inserted. Experimental results show that inserted delay elements by the proposed algorithm are 59.0% fewer and the height of clock trees are 40.4% shorter on average than those by a straightforward algorithm. The proposed algorithm can also be used to minimize the clock period, thus obtaining 19.0% shorter clock periods on average.