An information recording disk having a structure that a ring-shaped recording region is divided into a plurality of concentric, annular blocks, each of the blocks is divided in a circumferential direction into a plurality of equal sectors, and a recording track and a pit train for generating a header signal are previously formed in the recording region so that the recording density of a block increases as the block is nearer to the outer circumference of the recording region, is disclosed in which disk the recording region has a portion where blocks are pre-formatted so that the pit pitch of the header-signal generating pit train formed on the innermost recording track of the outer one of two adjacent blocks is greater than the pit pitch of the header-signal generating pit train formed on the innermost recording track of the inner block.