PURPOSE: An optical disk is provided to reduce circuit size of an optical writing/reading apparatus and stably read. CONSTITUTION: The optical disk comprises rewritable a first writing region and read only a second writing region. The first writing region includes a first track consisted a groove track consisted a plurality of grooves and a land track consisted a plurality of spaces between the grooves. The groove track and the land track are alternately formed on an optical disk substrate with a spiral or a concentric circle type. The first track is divided a plurality of first sectors. Each one of the first sectors has a first header region having a discrimination data to discriminate the first sector and a first data region writing a user data by forming a writing mark.
