A battery pack to be externally attached to a system body of a portable computer contains a plurality of batteries in two rows. A groove is formed on that portion of the top of the battery pack which correspond to the region between the rows of batteries. A hinge unit for swingably supporting a display unit is provided on the rear end of the system body of the computer in a manner such that it is partially housed in the groove of the battery pack. With this arrangement, the computer is reduced in thickness. The battery pack, which is connected to the rear end of the system body, is rotatable relatively to the system body. During use of the computer, therefore, a keyboard can be slightly declined toward a user by rotating the battery pack to raise the rear end of the system body.