A print data controlling method in which print data regarding a print request which has been issued from a terminal device is temporarily spooled in a print queue of a server and supplied from the print queue to a printer the print request comprising the print data and data representative of characteristics of print data, comprising the steps of: comparing print data regarding a current print request with print data which is previously spooled in the print queue; transmitting a result of the comparison to the terminal device which has issued the current print request; and generating a warning message in the terminal device when the result of the comparison indicates that print data identical with or similar to the print data regarding the current print request is previously spooled in the print queue, wherein the step of comparing the print data regarding the current print request with the print data previously spooled in the print queue is carried out by comparing the data representative of characteristics of print data, wherein the data representative of characteristics of print data includes size of the print data and user name, and wherein, when the comparison result indicates that print data identical with or similar to the print data regarding the current print request is previously spooled in the print queue, an input operation for designating a print data processing procedure of how to process the print data regarding the current print request and the previously spooled print data is accepted by the terminal device to which the comparison result was transmitted and the print data is processed according to the designated print data processing procedure, wherein a print data processing procedure of how to process the print data regarding the current print request and the previously spooled print data can be designated from among a plurality of previously-set print data processing procedures, and after a predetermined period of time has elapsed without designating of any particular print data processing procedure for the print data regarding the current print request and the already-spooled print data, the print data is processed according to a default print data processing procedure. comparing print data regarding a current print request with print data which is previously spooled in the print queue; transmitting a result of the comparison to the terminal device which has issued the current print request; and generating a warning message in the terminal device when the result of the comparison indicates that print data identical with or similar to the print data regarding the current print request is previously spooled in the print queue, wherein the step of comparing the print data regarding the current print request with the print data previously spooled in the print queue is carried out by comparing the data representative of characteristics of print data, wherein the data representative of characteristics of print data includes size of the print data and user name, and wherein, when the comparison result indicates that print data identical with or similar to the print data regarding the current print request is previously spooled in the print queue, an input operation for designating a print data processing procedure of how to process the print data regarding the current print request and the previously spooled print data is accepted by the terminal device to which the comparison result was transmitted and the print data is processed according to the designated print data processing procedure, wherein a print data processing procedure of how to process the print data regarding the current print request and the previously spooled print data can be designated from among a plurality of previously-set print data processing procedures, and after a predetermined period of time has elapsed without designating of any particular print data processing procedure for the print data regarding the current print request and the already-spooled print data, the print data is processed according to a default print data processing procedure.