A volume control apparatus that is connectable to a controller and controls a volume value of a sound signal based on an instruction from the controller includes a receiving section for, when a controller-side volume setting value settable in the controller is changed by a user's operation, receiving the changed controller-side volume setting value from the controller. The apparatus also includes a first difference value calculating section for calculating a first difference value between the changed controller-side volume setting value and the controller-side volume setting value before change, a second difference value calculating section for calculating a second difference value between a maximum volume value controllable by the controller and a current volume value, and an increase value calculating section for multiplying the second difference value by a ratio of the first difference value so as to calculate an increase value of the volume value.