A method for producing polymer oriented crystals, the method comprising: preparing an oriented melt by subjecting a polymer melt to elongation at a strain rate equal to or greater than a critical elongation strain rate so as to put the polymer melt in an oriented melt state; and rapidly cooling the polymer oriented melt, which is obtained in the step of preparing it, to crystallize it while keeping the oriented melt state, wherein the critical elongation strain rate is a critical elongation strain rate ε* defined as I or II below: I A critical elongation strain rate ε* determined in such a manner that a disc-shaped polymer melt of x 0 in radius and Δz 0 in thickness is sandwiched between transparent boards (1, 2), the polymer melt is rapidly cooled at a cooling rate of 20°C/min or faster to a constant temperature at which the polymer melt is kept supercooled wherein the degree of supercooling ΔT is 20K or greater, the polymer melt is pressed by the transparent boards in a thickness direction at a constant rate v, a critical point radius x* at which the polymer melt is turned into an oriented crystal is measured, and the critical elongation strain rate ε* is calculated from an equation ε* = αx* 3 where α = v/(2x 0 3 Δz 0); II A critical elongation strain rate ε* determined in such a manner that a rectangular-shaped polymer melt of x' 0 in center distance and Δz 0 in thickness and with a constant width is sandwiched between transparent boards (1, 2), the polymer melt is rapidly cooled at a cooling rate of 20°C/min or faster to a constant temperature at which the polymer melt is kept supercooled wherein the degree of supercooling ΔT is 20K or greater, the polymer melt is pressed by the transparent boards in a thickness direction at a constant rate v, a critical point center distance x'* at which the polymer melt is turned into an oriented crystal is measured, and the critical elongation strain rate ε* is calculated from an equation ε* = αx' * 2 where α = v/(2x' 0 2 Δz 0). preparing an oriented melt by subjecting a polymer melt to elongation at a strain rate equal to or greater than a critical elongation strain rate so as to put the polymer melt in an oriented melt state; and rapidly cooling the polymer oriented melt, which is obtained in the step of preparing it, to crystallize it while keeping the oriented melt state, wherein the critical elongation strain rate is a critical elongation strain rate ε* defined as I or II below: I A critical elongation strain rate ε* determined in such a manner that a disc-shaped polymer melt of x 0 in radius and Δz 0 in thickness is sandwiched between transparent boards (1, 2), the polymer melt is rapidly cooled at a cooling rate of 20°C/min or faster to a constant temperature at which the polymer melt is kept supercooled wherein the degree of supercooling ΔT is 20K or greater, the polymer melt is pressed by the transparent boards in a thickness direction at a constant rate v, a critical point radius x* at which the polymer melt is turned into an oriented crystal is measured, and the critical elongation strain rate ε* is calculated from an equation ε* = αx* 3 where α = v/(2x 0 3 Δz 0); II A critical elongation strain rate ε* determined in such a manner that a rectangular-shaped polymer melt of x' 0 in center distance and Δz 0 in thickness and with a constant width is sandwiched between transparent boards (1, 2), the polymer melt is rapidly cooled at a cooling rate of 20°C/min or faster to a constant temperature at which the polymer melt is kept supercooled wherein the degree of supercooling ΔT is 20K or greater, the polymer melt is pressed by the transparent boards in a thickness direction at a constant rate v, a critical point center distance x'* at which the polymer melt is turned into an oriented crystal is measured, and the critical elongation strain rate ε* is calculated from an equation ε* = αx' * 2 where α = v/(2x' 0 2 Δz 0). I A critical elongation strain rate ε* determined in such a manner that a disc-shaped polymer melt of x 0 in radius and Δz 0 in thickness is sandwiched between transparent boards (1, 2), the polymer melt is rapidly cooled at a cooling rate of 20°C/min or faster to a constant temperature at which the polymer melt is kept supercooled wherein the degree of supercooling ΔT is 20K or greater, the polymer melt is pressed by the transparent boards in a thickness direction at a constant rate v, a critical point radius x* at which the polymer melt is turned into an oriented crystal is measured, and the critical elongation strain rate ε* is calculated from an equation ε* = αx* 3 where α = v/(2x 0 3 Δz 0); II A critical elongation strain rate ε* determined in such a manner that a rectangular-shaped polymer melt of x' 0 in center distance and Δz 0 in thickness and with a constant width is sandwiched between transparent boards (1, 2), the polymer melt is rapidly cooled at a cooling rate of 20°C/min or faster to a constant temperature at which the polymer melt is kept supercooled wherein the degree of supercooling ΔT is 20K or greater, the polymer melt is pressed by the transparent boards in a thickness direction at a constant rate v, a critical point center distance x'* at which the polymer melt is turned into an oriented crystal is measured, and the critical elongation strain rate ε* is calculated from an equation ε* = αx' * 2 where α = v/(2x' 0 2 Δz 0).