The goal of the present research is to improve a quality of life of the elderly with a dementia. In this paper, it is realized by developing the dialog system that is controlled by three kinds of modules such as speech recognition engine, graphical agent, or database classified by a nursing schedule. The system was evaluated in an actual environment of a nursing facility by introducing it to an older male patient with dementia. The comparison study between dialog system and professional caregivers was then carried out at nursing home for 5 days in each case. The evaluation results showed that the dialog system was more responsive in catering to needs of dementia patient than professional caregivers. Moreover, the proposed system led the patient to talk more than caregivers did.