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, in comparison with constant angular velocity type, 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.