The purpose of this study is to verify the effect of the Happy Fatherhood Training Program on parenting stress, parenting efficacy, and paternal participation in parenting at early childhood stage. To this end, the study subjects consisted of 20 fathers with children in early childhood years, 10 people each in the experimental group and the control group. A total of eight sessions were conducted twice a week for 90 minutes. To verify the effectiveness of the program, the experiment-control group pre-identity verification and covariance analysis (ANCOVA) were conducted. The results of this study can be summarized as follows: first, the Happy Fatherhood Training Program had a significant effect on reducing the parenting stress of fathers with children in early childhood; second, the fathers’ parenting efficacy was significantly increased; and third, the fathers’ participation in parenting increased. Based on the results of the analysis, it is concluded that the Happy Fatherhood Training Program is an effective program that can reduce the parenting stress of fathers with children in early childhood and increase parenting efficacy and participation in parenting. Finally, limitations of the current study and recommendations for future research were discussed.