The purpose of this study was to examine the effects of the number of repetition of a prospective memory task (PMT), the length of the delay interval, and the degree of difficulty of the gross motor task on the PMT performance by using the Einstein-type experimental paradigm. In Experiment 1, each of twenty-five participants repeatedly performed the PMT that 2, 4, 8 and 12 min after initiation of the stepping task. In Experiment 2, one hundred participants were randomly assigned to one of the four conditions. In each condition, the PMT was performed only once. Results of Experiment 1 showed that the PMT performance increased as the number of repetition of the PMT increased with the 2-min delay interval having the poorest performance. Results of Experiment 2 showed that the 4-min delay led to the poorer PMT performance than the 2-min delay interval. In both experiments, the PMT performance was positively correlated to the stepping performance, while the PMT performance was negatively correlated to each of task difficulty and RPE. It was concluded that when the PMT was performed only once, the PMT performance decreased as a function of delay interval. When the PMT was repeatedly performed, however, the PMT performance increased as a function of repetition regardless of delay interval.