Outputs of a pulse sensor, a brain wave sensor, a conductivity sensor and an acceleration sensor are input to respectively corresponding condition detecting means, and the condition of the wearer (biological information, motion) is detected by the condition detecting means. The condition determining means determines the operation mode of the hearing aid from the condition of the wearer according to predetermined algorithm. Operation mode control portion drives an earphone based on the operation mode. By this, the characteristics of the hearing aid can be varied adapting to the wearer's condition.