Detective Conan Main Theme on Melodica (music instrumental) 

The Detective Conan Case Closed BGM is an integral part of the series, providing an atmospheric backdrop to the suspenseful and dramatic events. The BGM is composed by Katsuo Ono, who has worked on numerous anime series and features a mix of orchestral and electronic elements.
The music instrumental I use in this video calls as Melodica. It's a small, keyboard instrument that's played by blowing into a mouthpiece and pressing the keys. It produces sound through reeds that vibrate when air passes over them. Melodica is also commonly used in a variety of musical genres, including reggae, ska, and folk music.