1. An information processing system comprising: an extracting part configured to extract one or more devices in which the same phenomenon as that occurred in a maintenance target device had occurred from multiple managed object devices; an index-value calculating part configured to acquire device information on a device state of the maintenance target device and to calculate an index value regarding the device state of the maintenance target device, and to acquire pieces of device information on respective device states of the one or more devices and to calculate index values regarding the respective device states of the one or more devices; a first-similarity calculating part configured to calculate a first similarity between the index value of the maintenance target device and the index value of each of the one or more devices; a second-similarity calculating part configured to acquire environment information on a usage environment of the maintenance target device and pieces of environment information on respective usage environments of the one or more devices, and to calculate a second similarity between the environment information of the maintenance target device and the environment information of each of the one or more devices; and a presuming part configured to determine one or more reference devices from among the one or more devices on the basis of the first and second similarities, and to presume a replacement part of the maintenance target device on the basis of replacement parts that the one or more reference devices used for elimination of the phenomenon.