Patent ID: 7882709

Claim:
A glass substrate for an information recording medium, the substrate comprising: a disk shaped glass substrate having a center hole, containing at least Na 2 O as a composition thereof, and including, on an outer circumferential end face and an inner circumferential end face, regions which are chemically reinforced with a chemically-reinforcing treatment liquid containing a K + ion, wherein the following relationship is satisfied: 1≦( W 1 −W 3)/ W 2≦5 wherein: W1 is a maximum value of a K + ion concentration at a central portion in a thickness direction of the glass substrate, in the chemically reinforced regions on the outer circumferential end face and the inner circumferential end face; W2 is an Na + ion concentration at a position at which the K + ion concentration is the maximum value W1; and W3 is a K + ion concentration at the central portion in a thickness direction of the glass substrate and in a not chemically-reinforced region of the glass substrate.