A phase change optical recording medium is disclosed including at least a supporting substrate, and recording layer essentially consisting of AgInSbTe alloy compositions feasible of implementing recording and readout steps utilizing the change in reflectivity. The recording medium is characterized by the relation v 0 ≥ 0.7 v WH , where the critical relative velocity of phase change, v 0 , defined by the value of v, at which the differential coefficient, - dR (v) /dv, reaches a maximum, when the recording medium moves against an optical unit during the recording steps at a relative velocity, v, ranging from minimum and maximum relative velocities warranted for the recording medium, V WL and V WH , respectively. In addition, when the reflectivity is measured with varying erase power P E at the linear relative scanning velocity v 0 , the reflectivity of the recording layer as a function of erase power, R(P E ), preferably has a minimum. The recording layer included in the recording medium is devised to have an activation energy of deterioration of equal to, or larger than 1.6 eV, which is obtained by measuring asymmetry, A, and calculating according to the equations, k = dt/ dA, and k = k 0 x exp(E a /k B T). The recording medium is also characterized by activation energy of displacement of the boundary, ranging from 1.0 eV to 2.4 eV, which is obtained from the rate of decrease in the area, S, of the amorphous regions as recorded marks with time according to Arrhenius' equation.