To check whether recorded data are user data or not when being reproduced without adding any change when using a recording medium.

A CPU14 makes initialization (S3) and reports its finish to a host computer (S4). It starts De-ice which is dummy data recording (S5) and sets De-ice bits to 1. Then it checks on the instruction of the host computer for user data recording (S6). When it finds an instruction for user data recording, it sets the De-ice bits to zero to record the user data (S7) and updates a bitmap (S8). On the other hand, when there in no instruction for user data recording, it checks whether the background formatting is finished or not (S9), and if not, returns to the process of the step 6 after updating LWA (S10). However, when the formatting is over, it finishes this process.