A parameter adjustment apparatus for adjusting values of a plurality of parameters, pertaining to audio signal processing, on the basis of touch operation on a touch-panel type display device capable of identifying multipoint contacts, said parameter adjustment apparatus comprising: a display control section which displays, on the touch-panel type display device, a plurality of parameter images for selecting respective parameters of said plurality of parameters; a selection section (10, S2, S4, S5, S6) which, when start of a first touch operation on any one of the parameter images has been detected while no touch operation is being performed on the touch-panel type display device, starts selection of the respective parameter represented by the parameter image touched by the first touch operation, and which, when termination of the first touch operation has been detected, terminates the selection of said respective parameter, characterized in that the selection section (10, S1, S9) is further configured to keep said respective parameter selected until the first touch operation is terminated so that selection of any other parameter than said resepective parameter through another touch operation different from the first touch operation is made invalid, and in that said parameter adjustment apparatus further comprises: a change section (10, S1, S7, S8) which, when a second touch operation on the touch-panel type display device has been detected while said first touch operation is continuing, changes a value of said respective parameter, currently selected by said selection section, on the basis of a physical amount input via the second touch operation. a display control section which displays, on the touch-panel type display device, a plurality of parameter images for selecting respective parameters of said plurality of parameters; a selection section (10, S2, S4, S5, S6) which, when start of a first touch operation on any one of the parameter images has been detected while no touch operation is being performed on the touch-panel type display device, starts selection of the respective parameter represented by the parameter image touched by the first touch operation, and which, when termination of the first touch operation has been detected, terminates the selection of said respective parameter, characterized in that the selection section (10, S1, S9) is further configured to keep said respective parameter selected until the first touch operation is terminated so that selection of any other parameter than said resepective parameter through another touch operation different from the first touch operation is made invalid, and in that said parameter adjustment apparatus further comprises: a change section (10, S1, S7, S8) which, when a second touch operation on the touch-panel type display device has been detected while said first touch operation is continuing, changes a value of said respective parameter, currently selected by said selection section, on the basis of a physical amount input via the second touch operation. a change section (10, S1, S7, S8) which, when a second touch operation on the touch-panel type display device has been detected while said first touch operation is continuing, changes a value of said respective parameter, currently selected by said selection section, on the basis of a physical amount input via the second touch operation.