A musical sound control apparatus includes: an operator which as an index portion and changes values of a plurality of kinds of parameters by moving a position of the index portion; and a parameter control unit which executes processing of changing the values of the plurality of kinds of parameters according to an operated position as a position at which the index portion was moved from a standard position by an operation and processing of, when changing an assignment to the operator from a first parameter among the plurality of kinds of parameters to a second parameter among the plurality of kinds of parameters in a state in which the index portion is positioned at a position other than the standard position, setting a value of the second parameter assigned to a value which does not correspond to the position of the index portion.