In order to reveal the nozzle scaling law of a Repetitive Pulsed (RP) laser thruster, momentum-coupling coefficients of several conical nozzles were investigated by means of experiment and numerical analysis. In the experiment, a pendulum method was used to measure an impulse imparted to a conical nozzle by a laser-driven blast wave. A propagation of the blast wave in a conical nozzle and an exhaust-refill process were analyzed by CFD. The calculated Cm agreed with the experimental data. The processes until a critical time are qualitatively the same regardless of a divergence angle, but quantitatively different. As a result, the nozzle of a small apex angle enhances the performance of a RP laser thruster when only a single pulse is input.