A stud pin configured to be inserted into a stud pin installation hole in a tread portion of a pneumatic tire, the stud pin comprising: a tip end protruding from the tread portion to make contact with a road surface; and a buried base including a flanged bottom portion provided on an end opposite the tip end and extending in one direction; a flanged trunk portion provided between the bottom portion and the tip end; the buried base being embedded in the tread portion of the pneumatic tire in which the stud pin is installed, and pressure from a side surface of the stud pin installation hole on the bottom portion and the trunk portion securing the stud pin; the bottom portion including a plurality of first recesses formed on and along an outer peripheral surface thereof that comes into contact with the side surface of the stud pin installation hole; the trunk portion including a plurality of second recesses formed on and along an outer peripheral surface thereof that comes into contact with the side surface of the stud pin installation hole; and the first recesses provided on the bottom portion and the second recesses provided on the trunk portion being provided in the circumferential direction at a same peripheral position on the outer peripheral surface of the buried base wherein a first projection is formed between the first recesses on the periphery of the outer peripheral surface of the bottom portion of the buried base, and a shape of the first projection along the bottom portion is a first arc having a radius of curvature of R1 larger than half a maximum size of the bottom portion in a width direction orthogonal to the extending direction of the buried base, a ratio L1/L2 of a maximum size L1 of the bottom portion in a width direction to a maximum size L2 of the trunk portion in the width direction is greater than 1.0 and less than or equal to 1.5, the width direction being orthogonal to the extending direction of the buried base, a ratio L2/L3 of the maximum size L2 of the trunk portion in the width direction to a maximum size L3 of the tip end in the width direction orthogonal to the extending direction of the buried base of the stud pin is not less than 1.5 and not greater than 3.5, upon the extending direction of the buried base of the stud pin being a height direction, a height from a bottom surface of the bottom portion of the buried base opposite the tip end is H1, and a height from the bottom surface to a top end of the bottom portion is H2, and a ratio H1/H2 of the height H1 to the height H2 is from 6.0 to 9.0. a tip end protruding from the tread portion to make contact with a road surface; and a buried base including a flanged bottom portion provided on an end opposite the tip end and extending in one direction; a flanged trunk portion provided between the bottom portion and the tip end; the buried base being embedded in the tread portion of the pneumatic tire in which the stud pin is installed, and pressure from a side surface of the stud pin installation hole on the bottom portion and the trunk portion securing the stud pin; the bottom portion including a plurality of first recesses formed on and along an outer peripheral surface thereof that comes into contact with the side surface of the stud pin installation hole; the trunk portion including a plurality of second recesses formed on and along an outer peripheral surface thereof that comes into contact with the side surface of the stud pin installation hole; and the first recesses provided on the bottom portion and the second recesses provided on the trunk portion being provided in the circumferential direction at a same peripheral position on the outer peripheral surface of the buried base wherein a first projection is formed between the first recesses on the periphery of the outer peripheral surface of the bottom portion of the buried base, and a shape of the first projection along the bottom portion is a first arc having a radius of curvature of R1 larger than half a maximum size of the bottom portion in a width direction orthogonal to the extending direction of the buried base, a ratio L1/L2 of a maximum size L1 of the bottom portion in a width direction to a maximum size L2 of the trunk portion in the width direction is greater than 1.0 and less than or equal to 1.5, the width direction being orthogonal to the extending direction of the buried base, a ratio L2/L3 of the maximum size L2 of the trunk portion in the width direction to a maximum size L3 of the tip end in the width direction orthogonal to the extending direction of the buried base of the stud pin is not less than 1.5 and not greater than 3.5, upon the extending direction of the buried base of the stud pin being a height direction, a height from a bottom surface of the bottom portion of the buried base opposite the tip end is H1, and a height from the bottom surface to a top end of the bottom portion is H2, and a ratio H1/H2 of the height H1 to the height H2 is from 6.0 to 9.0.