An earphone includes an audio transmitter, a housing, a sound passage pipe, a radiator, and a light receiver. The audio transmitter transmits sound. The housing has an internal space for containing the audio transmitter. The sound passage pipe guides sound produced at the audio transmitter into an external auditory canal. The radiator radiates light into the external auditory canal. The light receiver is disposed in the internal space of the housing. The light receiver converts the light into a signal, the light having been reflected off the external auditory canal and passed through an internal space of the sound passage pipe. The housing, the sound passage pipe, and the radiator are disposed in this order.