This invention provides a particle size distribution measuring apparatus, which has a function of informing an operator of a procedure of validation work of the particle size distribution measuring apparatus. A storage medium which records validation data providing a procedure of validation work for the particle size distribution measuring apparatus and a control unit which has a validation help function which successively reads a validation procedure from the validation data and controls the particle size distribution measuring apparatus according to a measuring procedure without any operation by an operator in the validation procedure while teaching the operator a work procedure requiring an operation by the operator.