A USB management system using a USB relay device includes a management terminal having a management database for recording management information of a USB client registered in advance. The USB relay device has a connection switching unit for switching a connection state between a first connector portion to which the USB client is connected and a second connector portion which is connected to a USB host controller. When the USB client is connected to the first connector portion, the USB relay device reads management information of the USB client and transmits the management information to the management terminal, and the management terminal inquires of the management database about the management information of the USB client transmitted from the USB relay device, compares the management information with the management information of the USB client registered in advance, and determines the connection state by the connection switching unit.