Abstract: A headset for a helmet transmits audio signals using bone conduction, and transmits audio signals even when not using bone conduction. A headset for a helmet for transmitting audio signals to a user wearing a helmet includes: a bone conduction oscillator which receives the audio signals and emits audio oscillations; an arm part which has the bone conduction oscillator on the leading end side thereof; and an attachment part which attaches the base end side of the arm part on the outer side of the crown of the helmet in a rotatable manner. The bone conduction oscillator is brought into contact with either the head portion of the user or the outer side of the crown, depending on the angle of rotation a of the arm part. The audio signals are thus transmitted to the user when bone conduction is not used by using sounds emitted by the crown.