To provide an excellent input property through keys and also portability that is the same as a portable computer which does not have an extension battery attaching function in spite of being able to attach battery, in a portable computer device to which extension battery can be attached.

This device consist of a portable computer body 1 and extension battery 4 which is attached to the rear of the body in an attachable and detachable way, and the battery 4 has the form of a wedge shape which corresponds to a wedge-shaped gap that is formed between the rear of the body and the plane on which the body is placed when the body is slanted with the bottom of the tip of the front side of the body 1 as an axis, and the top of the body becomes slanted with the front side lowered when the battery 4 is attached.