Problem solving process consists not only of combining and applying existing operators but also acquiring new operators. To show quantitative aspects of this acquisition process of operators, 42 subjects were required to solve the sliding the puzzle named 8-puzzle. The solving process of this puzzle was described and analyzed in terms of latency pattern and subjects' self-reports concerning how they solved the puzzle. The results showed that subjects acquired more effective operators as they underwent successive tasks and the perception of the board configuration changed as a function of operator acquisition.