Recently, a lot of multiple packaged unit system is adopted in small to medium sized buildings in Japan. This system enables to control each packaged air conditioner (PAC) individually because multiple packaged units are placed decentrally. However, it is not clarified sufficiently how indoor environment is formed when PAC is working. This paper shows the measurement results of indoor thermal environment in a medium sized building with PAC in all season for the purpose of clarifying the current status of indoor environment and its issue. In indoor thermal environment, there was no issue throughout the year though measurement conditions made difference in temperature and humidity distribution. In indoor units operation, it was clarified that supply air temperature of PAC is different from each PAC and way. In addition, it was clarified that short circuit of supply air from PAC to inlet of the ventilation devices happen.