A usage information management system for managing information on usage of diaper products, comprising: a first reading device for reading a product model type indicating a kind of diaper product (2, 6), which is stored in advance in an IC chip of said diaper product (2, 6) provided with an IC tag where information can be read out from said IC chip through an antenna for radio communication; a second reading device for reading a wearer identification number for discriminating one wearer of a diaper product (2, 6) from other wearers in a predetermined manner; a wearer database storage part for storing a wearer database which is a set of data elements each associating said wearer identification number with an applicable model type, latest wearing date and time and a change interval, said applicable model type is a product model type of a diaper product (2, 6) to be put on a wearer corresponding to said wearer identification number; and a model type check part for, when one diaper product (2, 6) is put on a wearer, specifying a data element in said wearer database, which includes a wearer identification number read out by said second reading device, and checking an applicable model type in said data element with a product model type of said diaper product (2, 6) read out by said first reading device; a wearer database updating part for, when a change of applicable model type of a diaper product (2, 6) to be put on a wearer is needed, specifying a data element in said wearer database, which includes a wearer identification number read out by said second reading device, and updating a value of applicable model type in said data element to a product model type read out from a diaper product (2, 6) after changing by said first reading device, and when one diaper product (2, 6) is put on a wearer, said wearer database updating part specifies a data element in said wearer database, which includes a wearer identification number read out by said second reading device, and updates latest wearing date and time in said data element to date and time when said diaper product (2, 6) is put on; and a change-scheduled date and time output part for outputting next change-scheduled date and time for each wearer corresponding to said wearer identification number on the basis of said wearer identification number, said latest wearing date and time and said change interval. a first reading device for reading a product model type indicating a kind of diaper product (2, 6), which is stored in advance in an IC chip of said diaper product (2, 6) provided with an IC tag where information can be read out from said IC chip through an antenna for radio communication; a second reading device for reading a wearer identification number for discriminating one wearer of a diaper product (2, 6) from other wearers in a predetermined manner; a wearer database storage part for storing a wearer database which is a set of data elements each associating said wearer identification number with an applicable model type, latest wearing date and time and a change interval, said applicable model type is a product model type of a diaper product (2, 6) to be put on a wearer corresponding to said wearer identification number; and a model type check part for, when one diaper product (2, 6) is put on a wearer, specifying a data element in said wearer database, which includes a wearer identification number read out by said second reading device, and checking an applicable model type in said data element with a product model type of said diaper product (2, 6) read out by said first reading device; a wearer database updating part for, when a change of applicable model type of a diaper product (2, 6) to be put on a wearer is needed, specifying a data element in said wearer database, which includes a wearer identification number read out by said second reading device, and updating a value of applicable model type in said data element to a product model type read out from a diaper product (2, 6) after changing by said first reading device, and when one diaper product (2, 6) is put on a wearer, said wearer database updating part specifies a data element in said wearer database, which includes a wearer identification number read out by said second reading device, and updates latest wearing date and time in said data element to date and time when said diaper product (2, 6) is put on; and a change-scheduled date and time output part for outputting next change-scheduled date and time for each wearer corresponding to said wearer identification number on the basis of said wearer identification number, said latest wearing date and time and said change interval.