Six rhesus monkeys were tested for a change in reaction time for problem-solving during a learning-set task, in which they showed progressive improvement in the rate of learning successive problems of visual discrimination. To evaluate the processing time for cognitive processes in problem-solving, the differences in release latency and movement time between the visual discrimination task and the visuomotor control task were defined. In their first experience, the monkeys required several hundreds of trials for solving the problem, and the Δrelease latency was constant throughout the learning. With increasing experience, they solved problems within fewer trials than with the first problem. At this stage, the Δrelease latency was high at the beginning and then decreased. The rise in the Δrelease latency within the learning acquisition period increased depending on the amount of experience with problems they had solved, whereas the Δmovement time within that period was not significantly affected by the experience with problems. The present findings suggest that the number of problem-solving experiences could promote profound cognitive processing, which may be related to a conceptual representation that actualizes the flexibility of learning, namely, the learning set.