An in-ear earphone includes a shell and a sound output device. The shell has a first engaging portion. The sound output device has a sound tunnel, a second engaging portion and a speaker. The speaker is disposed between the sound tunnel and the second engaging portion coaxially with the sound tunnel. The second engaging portion is movably engaged with the first engaging portion. The angle between the shell and the sound output device is adjustable so that the sound tunnel can be suitably plugged into individual user's ear canals.