Noninvasive and low reactive level laser (LLLT) is used as one of the light therapies without giving pain to the patient. Therefore, it is used often clinically in pain treatment, orthopedics, plastic surgery, dermatology, and dentistry. In the pain clinic field, it is one of the procedures indispensable to treatment of various pain including postherpetic neuralgia, diabetic neuropathy or myofascial pain. In recent years the mechanism has been gradually elucidated by basic study. The action is on sensory nerve, sympathetic nerve, blood vessel, immunity, inflammation and central nervous system, and is thought to contribute to analgesia. Also, many reports such as action to inhibit "itch", a promotor action of the bone metabolism, and the follicular maturation acceleration action have tested and elucidated these mechanisms, and will add further adaptation that will be new in future. Furthermore, development and downsizing of the free electron laser will promote elucidation of the low response level laser therapy. We expect much in the future of the LLLT.