This study aims to examine professional development in teaching of beginning teachers according to increasing of teaching experiences through clarifying characteristics of Mr. A's thinking at his 1st year's teaching and at 4th year's teaching after employment. As a result, the percentages of each category about his thinking have changed and the complex category "Teacher's Behavior Based on Realities of Children" which consists of "Teachers' Teaching" and "Children's Leaning" has emerged. The following 5 points was guessed about Mr. A's profession for teaching in physical education according to the effects. 1. Mr. A was able to make a teaching plan with manifest intention and teaching intentionally. 2. Mr. A assessed children's leaning at once and taught them with thinking immediately in his action. 3. Mr. A justified instantly if he accepted children's speaking or not through interpreting the meaning of their speaking when they talked stories which he had not expected. 4. Mr. A checked the child's performance which he wanted to ask to demonstrate in next lesson while he made a program for next lesson. 5. Mr. A thought ahead children's learning in his teaching and made his lesson plan and taught them actually according to his anticipation.