Recording of data into a multilayer optical disk and reliable reproduction of the data are enabled. When user data are recorded on a multilayer optical disk having a first layer L0 and a second layer L1, the second layer L1 is formatted beforehand, to thus record dummy data. Subsequently, the user data are recorded into the first layer L0. Even after completion of recording of the user data at some point in the first layer L0, an area of the second layer L1 located immediately above or below a recorded area of the first layer L0 remains in a recorded state at all times. Compatibility with a play-only disk is maintained, and the play-only drive can reproduce the user data immediately after recording of the data.