A peripheral device driver installing device for installing a peripheral device driver peculiar to a peripheral device on an information processor which is connected to the peripheral device, comprising: a connection detecting unit for detecting a connection between the peripheral device and the information processor; a peripheral device inquiring unit for inquiring information concerning the peripheral device to the peripheral device; an installation determining unit for determining whether or not the peripheral device driver peculiar to the peripheral device has been installed on the information processor on the basis of the information concerning the peripheral device sent in response by the peripheral device to the peripheral device inquiring unit; a reading unit for reading a file of the peripheral device driver stored in the peripheral device if it is determined by the installation determining unit that the peripheral device driver has not been installed on the information processor; a storage unit for storing the file of the peripheral device driver read by the reading unit; a peripheral device driver installing unit for installing the peripheral device driver on the information processor on the basis of the file of the peripheral device driver stored in the storage unit; and a writing unit for writing the file of the peripheral device driver stored in the information processor on a storage unit provided in the peripheral device when the peripheral device and the information processor are disconnected.