This USB memory key casing exhibits an accessory accommodation housing (6) for a chip microcard (7) independent of the electronic components (4, 5) of the USB memory key. It allows the owner of a USB key and of a chip microcard (7) to have available a convenient location for accommodating the chip microcard (7). It also makes it possible to associate, in one and the same packaging, while being separable, an intelligent chip microcard and an electronic key that are dedicated to transactions pertaining to one and the same banking or other service, one by way of a specialized reading terminal hooked up to the computer system of the provider of the service and the other by way of a host electronic apparatus linked to the Internet network.