When a sub-track having burst data A and D, a sub-track having burst data A and C, a sub-track having burst data B and C, and sub-track having burst data B and D are repeatedly arranged in this order, in accordance with equations 1 and 2, a sub-track t included in a track T determines the value of a constant n within a range of 1.2 (inclusive) to 1.8 (inclusive) so as to obtain linearity between a position in a disc radial direction r and a head position P in a disc radial direction r in the sub-track t. Subsequently, the head position P is calculated using the determined constant n and equations 1 and 2: P=(A-B)*|A-B|(n-1)/(|A-B|n+|C-D|^n) (1) P=(C-D)*|C-D|(n-1)/(|A-B|n+|C-D|n) (2)