Written by Naoki Higashida, 'The Reason I Jump' topped The Sunday Times chart for hardback non-fiction last weekend.
His condition is so severe that he cannot speak. The book has now been translated into English to help parents of autistic children understand what they are going through.
Higashida, now 20, who lives with his family near Tokyo, said he was stunned by the success of his book.
"I was so surprised I could tumble down," Higashida wrote on his blog.
His own answers provide a rare insight into what the condition feels like and dispels many of the myths about autism, such as having an inability to understand others and disliking company, 'The Sunday Times' reported.
"As a person who cannot speak, I had thought that I should write so people can read my words and to know more about me. I thought that was a way for me to connect with the world. So I became a writer," Higashida wrote.
Since Higashida was unable to communicate, teachers created a cardboard alphabet grid and, over a period of years, taught him to point at letters.
