Japan is the most aged country in the world. The percentage of population aged 65 years or older will have exceeded 30% by 2025 and get close to 40% by 2060. As the population gets older, the prevalence of dementia, depression, delirium, and other mental health problems specific to late life is sharply increasing. For example, the prevalence of dementia is estimated to be seven million (20% in older population aged 65 years or older) in 2025. In 2019, the national government published the National Framework for Promoting Dementia Measures, planning a series of programs to realize the society where people can live well with dementia as well as where the onset of dementia can be delayed by 2025. Behavioral and psychological symptoms of dementia (BPSD) are one of crucial mental health issues addressed in this plan. As for depression in late life, comprehensive community-based approaches have been developed on the basis of the evidence regarding risk factors. These approaches have also contributed to reduction in the number of suicides in late life. Prevention and control of delirium is another important mental health issue in acute hospitals. Recently, mental health problems specific to the oldest-old have been noticed. They are often living alone, socially isolated, financially in need, and complicated with physical/psychiatric problems including cognitive impairment. Not only to prevent such a complex state but also to ensure human rights and mental health wellbeing, a new type of age- and dementia-friendly communities are needed to be established.