A hearing aid (101) comprises a microphone (121) converting sound into an electrical signal, a processor (105) disposed inside a main body case (102), a first volume adjuster (104) having a variable resistor, and a receiver (123) converting an electrical signal into sound. The processor (105) has an amplifier (135) amplifying an electrical signal from the microphone (121), a second volume adjuster (105b) setting a degree of amplification by the amplifier (135), and a controller (130) controlling the second volume adjuster (105b) and the amplifier (135). The controller (130) detects the resistance value of the variable resistor, determines whether or not the resistance value has exceeded a specific threshold, acquires a specific value for the degree of amplification by the amplifier (135), and sets the degree of amplification by the amplifier (135) to this specific value when the controller determines that the resistance value has exceeded the specific threshold.