The interactive service offers cognitive therapy sessions that identify a person's level of depression by asking questions about his or her sleeping and eating habits, weight change, and emotional well-being.
Using their mobile phones - which are also widely substituted in Japan as wallets, train tickets, books, and television - people can easily access the service.
"I think this can be helpful for people in times of need or when they feel a little blue, as a form of daily prevention against depression," Keio University Professor Yutaka Ohno, who launched the project, told AFP.
"For those who are already following medical treatment, it may act as a supplement," said Ohno, who spearheaded Cognitive Therapy in Japan, a type of psychotherapy first developed by American psychiatrist Aaron Beck in the 1960s.
Ohno has also treated Crown Princess Masako, who suffers from a stress-induced illness.
The service explains symptoms of depression but warns that it is not a substitute for treatment and encourages users to consult a doctor if he or she is evaluated as having more than a mild depression.
It also features seven mini chapters that offer ways to change negative perceptions and techniques to "lighten" the heart such as problem-resolving, relaxation, taking action and self-assertion.
Over the past decade, Japanese society has broken down taboos surrounding depression, but psychotherapy is still relatively new. Depression is euphemistically referred to as "the heart flu."
About 900,000 Japanese receive medical treatment for depression, but the number of people suffering from the illness is believed to be much higher.
Japan also has one of highest suicide rates in the world - more than 30,000 in 2007.
"Psychotherapy is not widespread in Japan. This is mostly because hospitals focus on treating depression clinically and psychotherapy is not covered by the medical insurance plan," said Ohno.
"The number of psychotherapy specialists and doctors is far from sufficient."