A sound processing apparatus includes a signal processing device that individually performs first localization setting (e.g., sound volume panning) for setting localization of an input sound signal based on a value of a first parameter and second localization setting (e.g., delay panning) for setting localization of the input sound signal based on a value of a second parameter. In response to an adjustment by an operation device of the value of one of the first and second parameters, a control device automatically changes the value of the other of the first and second parameters. In this way, sound image localization based on the first localization setting and sound image localization based on the second localization setting are automatically controlled in an interlocked relation to each other. At least one of the sound signals localized based on the first and/or second localization setting is output to an output destination.