Boku no Natsuyasumi 4 (ぼくのなつやすみ4, lit. "My Summer Vacation 4: Boy’s Inland Detective Club, Me and the Secret Map") is a video game developed by Millennium Kitchen and published by Sony Computer Entertainment for the PlayStation Portable. It is part of the popular Boku no Natsuyasumi series and was released in Japan on July 2, 2009. Like Boku no Natsuyasumi 2, it takes place in a Japanese coastal village.
The main character spends his summer vacation in a coastal village in Japan. The games contains the familiar bug collecting, beetle fighting, swimming, fishing, morning exercises, and family meals from previous series entries, but also features new activities, such as playing a taiko drum, challenging other children to duels with your mechanical toys, a beetle circus, and several table top games. Unlike other games in the series, taking place in the year 1975, this installment takes place in the summer of 1985.