The present invention relates to method and apparatus for controlling disk reproduction speed to extend an operable time of a portable device such as a notebook computer using a battery as a power source. A method for adjusting a disk reproduction speed based on a remaining battery energy according to the present invention, at the part of a portable device such as a notebook computer, detects an amount of the remaining battery energy, and sends a data indicating the detected amount of the remaining battery energy to a connected disk device, and, at the other part of a disk device, reduces a disk reproduction speed based on the data sent by the portable device. The method and apparatus for controlling disk reproduction speed according to the present invention can extend an operable time of the portable device whose operating power is supplied from an equipped battery whose storage capacity is restricted.