A malfunction condition judgment apparatus (MCJA) that judges malfunction condition (MC) of an observed object based on a change of observed values. The MCJA acquires time series data for values of each of a plurality of variables; calculates, with respect to each of the variables, a statistic defining a probability density function of that variable at T1, based on the value of that variable at T1 and that statistic at a point of time prior to T1; calculates dissimilarity showing an extent of variation between the statistic calculated for each variable and a statistic of a criterial probability density function predetermined corresponding to that variable; and picks, out of the plurality of variables, a variable for which the calculated dissimilarity is larger than a predetermined reference value, as the variable by which MC of the observation object is detected.