A deterioration diagnosing device of a rolling equipment machine includes an input/output data obtaining unit, a model identifying unit, a monitoring parameter calculating unit, a monitoring parameter usage determining unit, a representative value calculating unit, a representative value storage unit, and a deterioration diagnosing unit. The monitoring parameter usage determining unit includes a categorized monitoring parameter acquiring function for acquiring the monitoring parameters, so as to be classified according to categories designated depending on a rolling condition. The representative value calculating unit calculates a representative value of monitoring parameters from a predetermined time period corresponding to each of the categories. The representative value storage unit accumulates, with respect to each of the categories, the representative values over a learning period designated from a start of a monitoring process. The deterioration diagnosing unit includes a categorized deterioration determining function that determines presence/absence of deterioration with respect to each of the categories.