A gear device of a timepiece, comprising: a wheel provided with a hole in a center portion of the wheel, the hole having distances from a rotation center to an inner edge, and the distances being different in accordance with angular positions about the rotation center; and an arbor including an insertion portion fitted into the hole, the insertion portion having distances from the rotation center to an outer edge, and the distances being different in accordance with angular positions about the rotation center, wherein the hole includes at least a first portion and a second portion that are positioned in a circumferential direction about the rotation center and contact the insertion portion, and a further portion that is positioned between the first portion and the second portion in front of the first portion and the second portion in a specific rotation direction about the rotation center and has a distance from the rotation center longer than a distance from the rotation center to each of the first portion and the second portion, wherein the insertion portion is a gear-like portion having a distance ra from the rotation center to an outermost projecting edge, the hole has distances Ra, Rb from the rotation center to the inner edge, the distance Ra being different from the distance Rb, and characterised in that the distance ra, the distances Ra, Rb of the hole, and an angle θ satisfy a following inequation where the angle θ is an angle between a line connecting the rotation center and a center of a tooth bottom of a tooth of the gear-like portion and a line connecting the rotation center and the outmost projecting edge: Rb < ra < Rb / cos θ ≤ Ra. a wheel provided with a hole in a center portion of the wheel, the hole having distances from a rotation center to an inner edge, and the distances being different in accordance with angular positions about the rotation center; and an arbor including an insertion portion fitted into the hole, the insertion portion having distances from the rotation center to an outer edge, and the distances being different in accordance with angular positions about the rotation center, wherein the hole includes at least a first portion and a second portion that are positioned in a circumferential direction about the rotation center and contact the insertion portion, and a further portion that is positioned between the first portion and the second portion in front of the first portion and the second portion in a specific rotation direction about the rotation center and has a distance from the rotation center longer than a distance from the rotation center to each of the first portion and the second portion, wherein the insertion portion is a gear-like portion having a distance ra from the rotation center to an outermost projecting edge, the hole has distances Ra, Rb from the rotation center to the inner edge, the distance Ra being different from the distance Rb, and characterised in that the distance ra, the distances Ra, Rb of the hole, and an angle θ satisfy a following inequation where the angle θ is an angle between a line connecting the rotation center and a center of a tooth bottom of a tooth of the gear-like portion and a line connecting the rotation center and the outmost projecting edge: Rb < ra < Rb / cos θ ≤ Ra.