In a diagnosis apparatus for diagnosing a state of a plasma processing apparatus, prior distribution information including a probability distribution function is previously obtained for each of first sensors by using first sensor values obtained by the first sensors in a first plasma processing apparatus, a probability distribution in each of second sensors corresponding to each of the first sensors is estimated based on the previously obtained prior distribution information and second sensor values obtained by the second sensors in a second plasma processing apparatus different from the first plasma processing apparatus, and a state of the second plasma processing apparatus is diagnosed by using the estimated probability distribution.