Glass plate processing method and glass plate

A glass plate processing method for dividing a glass plate by a separation line that divides a main surface of the glass plate into two regions, the method comprising:

• forming a crack that extends from the separation line diagonally with respect to the main surface, in a cross-section that is orthogonal to the separation line by moving upon the glass plate, along the separation line, an irradiation point of a first laser beam having a power density converted from a first photon density that is less than 1×108 W/cm2;
• after the crack is formed, forming a modified portion in the cross-section, on a virtual line that extends in a direction perpendicular to the main surface, from a tip of the crack towards a center of a thickness of the glass plate by moving upon the glass plate, along the separation line, an irradiation point of a second laser beam having a power density converted from a second photon density that is greater than 1×108 W/cm2, the second photon density is a density of a pulse laser beam having a width of 1000 nm or less;
• and
• after the modified portion is formed, applying stress to the glass plate and forming a new crack that spans from the tip of the crack to the modified portion.