A contact lens including an optical portion in a center section and a periphery portion situated peripherally thereto, wherein: the optical portion is formed on front and rear surfaces devoid of a biased center of gravity resulting from creating a prism; the periphery portion is provided with an upper thin portion and a lower thin portion formed to respectively extend with unchanging thickness dimension in a circumferential direction in sections that during wear are situated in opposition in a vertical direction, while being provided with a pair of thick portions having greater thickness dimension than the thin portions (42, 44), which are formed to respectively extend with unchanging thickness dimension in the circumferential direction in sections that during wear are situated in opposition in a horizontal direction; the pair of thick portions each extend in the circumferential direction to both upper and lower sides across a horizontal radial direction line that during wear extends in the horizontal direction, with the thick portions extending for a greater distance to the lower side than to the upper side of the horizontal radial direction line, thereby biasing downward a location of a gravity center of the thick portion; upper transition portions are provided in sections to both circumferential sides of the upper thin portion such that the upper transition portions become progressively thinner going in the circumferential direction towards the upper thin portion from upper edges of the thick portions, respectively; lower transition portions are provided in sections to both circumferential sides of the lower thin portion such that the lower transition portions become progressively thinner going in the circumferential direction towards the lower thin portion from lower edges of the thick portions, respectively; the contact lens being characterised in that: the value of rate of thickness change in each lower transition portion expressed as a ratio of change in thickness dimension to circumferential length thereof, is greater than the value of rate of thickness change in each upper transition portion expressed as the ratio of change in thickness dimension to circumferential length thereof; and center angle: α of the upper transition portions about the lens center axis is within a range between 40 degrees and 60 degrees, and a center angle: β of the lower transition portions about the lens center axis is within a range between 30 degrees and 50 degrees. the optical portion is formed on front and rear surfaces devoid of a biased center of gravity resulting from creating a prism; the periphery portion is provided with an upper thin portion and a lower thin portion formed to respectively extend with unchanging thickness dimension in a circumferential direction in sections that during wear are situated in opposition in a vertical direction, while being provided with a pair of thick portions having greater thickness dimension than the thin portions (42, 44), which are formed to respectively extend with unchanging thickness dimension in the circumferential direction in sections that during wear are situated in opposition in a horizontal direction; the pair of thick portions each extend in the circumferential direction to both upper and lower sides across a horizontal radial direction line that during wear extends in the horizontal direction, with the thick portions extending for a greater distance to the lower side than to the upper side of the horizontal radial direction line, thereby biasing downward a location of a gravity center of the thick portion; upper transition portions are provided in sections to both circumferential sides of the upper thin portion such that the upper transition portions become progressively thinner going in the circumferential direction towards the upper thin portion from upper edges of the thick portions, respectively; lower transition portions are provided in sections to both circumferential sides of the lower thin portion such that the lower transition portions become progressively thinner going in the circumferential direction towards the lower thin portion from lower edges of the thick portions, respectively; the contact lens being characterised in that: the value of rate of thickness change in each lower transition portion expressed as a ratio of change in thickness dimension to circumferential length thereof, is greater than the value of rate of thickness change in each upper transition portion expressed as the ratio of change in thickness dimension to circumferential length thereof; and center angle: α of the upper transition portions about the lens center axis is within a range between 40 degrees and 60 degrees, and a center angle: β of the lower transition portions about the lens center axis is within a range between 30 degrees and 50 degrees. the value of rate of thickness change in each lower transition portion expressed as a ratio of change in thickness dimension to circumferential length thereof, is greater than the value of rate of thickness change in each upper transition portion expressed as the ratio of change in thickness dimension to circumferential length thereof; and center angle: α of the upper transition portions about the lens center axis is within a range between 40 degrees and 60 degrees, and a center angle: β of the lower transition portions about the lens center axis is within a range between 30 degrees and 50 degrees.