We determined how the room layout of an apartment and its natural cross ventilation affect overall indoor climatic comfort during the summer in Japan. To do this, we carried out three investigations at a corporate apartment complex: (1) a questionnaire on the degree of satisfaction concerning general dwelling environment, (2) a measurement of indoor climate with natural cross ventilation present, and (3) a survey on the use of air conditioning. We used such methodology because the way of living, as well as the occupants' psychological evaluation and the physical environment, are essential data for effectively evaluating the indoor climate with respect to room layout characteristics. The questionnaire clearly showed that natural cross ventilation, which influences indoor climate, affects on occupant's evaluation for having a comfortable dwelling environment. By comparing resultant indoor climate of three types of apartment floor plan, i.e., two side-corridor types and a staircase type, in terms of the standard new effective temperature (SET^*) and usage percentage of air conditioning, which were respectively determined from the indoor climate measurement and air conditioning survey, we found that the staircase type is more comfortable than the other types since it has the greatest velocity of indoor air flow. Regarding the way of living, the occupant interviews revealed that the restriction of natural cross ventilation at night due to privacy and security considerations made the dwelling environment extremely uncomfortable. Our results indicate that planning the thermal environment is an important factor affecting human standards of living.