The This study investigates the impacts of working time on life satisfaction using data from original large-scale survey questionnaires in Japan. The previous studies dealing with the relationship between working time and life satisfaction are limited to a study in Germany by Rätzel (2012), thus it is considered that an accumulation of studies in this field is necessary. Our study takes consideration of non-linearity in the relationship between working time and life satisfaction that was not considered in the previous study, using a semi-parametric method. In addition, taking advantage of the large-scale survey data, we investigate relationships by samples to find whether or not they are dependent upon respective individual characteristics such as age, gender, marital status, and whether or not both the husband and wife are working. Moreover, income, form of employment (regular employees, non-regular employees, self-employed, part-time, etc.), and business and industry categories are considered. Our results suggest that the relationship depends upon the individual attributes, the form of employment, and that it varies with each category in business, as well as each industry.