A female snap button with which a post of a male snap button is engageable and disengageable, the female snap button comprising: a first member (40, 70) at least partially defining an aperture (P40, P70) to which the post is inserted, the aperture (P40, P70) being capable of expanding in accordance with the insertion of the post and capable of recovering from the expanded aperture width to its initial aperture width; and a second member (10, 50, 60, 91) capable of restricting the expansion of the aperture (P40, P70) so as to increase the required force for engagement and disengagement between the post and the female snap button or so as to prohibit the post from engaging with and disengaging from the female snap button; wherein the second member (10, 50, 60, 91) comprises at least one contact portion (10m, 50m, 60m, 91m) that is to be in contact with the first member (40, 70), and the first member (40, 70) comprises at least one contacted portion (40m, 70m) that is to be contacted with the contact portion (10m, 50m, 60m, 91m); and wherein one of the first member (40, 70) and the second member (10, 50, 60, 91) is rotatable relative to the other member; wherein the extent of the expansion of the aperture (P40, P70) allowed by the second member (10, 50, 60, 91) varies in accordance with the relative position of the contact portion (10m, 50m, 60m, 91m) and the contacted portion (40m, 70m) in the circumferential direction that is around the insertion direction of the post into the aperture (P40, P70), the extent of the expansion of the aperture (P40, P70) allowed by the second member (10, 50, 60, 91) being adjustable in accordance with the rotation of one of the first member (40, 70) and the second member (10, 50, 60, 91) relative to the other, characterized in that when the contact portion (10m, 50m, 60m, 91m) and the contacted portion (40m, 70m) face one another, the post which has been inserted through the aperture (P40, P70) is prohibited from disengaging from the female snap button, and when the contact portion (10m, 50m, 60m, 91m) and the contacted portion (40m, 70m) do not face one another, the post which has been inserted through the aperture (P40, P70) is not prohibited from disengaging from the female snap button. a first member (40, 70) at least partially defining an aperture (P40, P70) to which the post is inserted, the aperture (P40, P70) being capable of expanding in accordance with the insertion of the post and capable of recovering from the expanded aperture width to its initial aperture width; and a second member (10, 50, 60, 91) capable of restricting the expansion of the aperture (P40, P70) so as to increase the required force for engagement and disengagement between the post and the female snap button or so as to prohibit the post from engaging with and disengaging from the female snap button; wherein the second member (10, 50, 60, 91) comprises at least one contact portion (10m, 50m, 60m, 91m) that is to be in contact with the first member (40, 70), and the first member (40, 70) comprises at least one contacted portion (40m, 70m) that is to be contacted with the contact portion (10m, 50m, 60m, 91m); and wherein one of the first member (40, 70) and the second member (10, 50, 60, 91) is rotatable relative to the other member; wherein the extent of the expansion of the aperture (P40, P70) allowed by the second member (10, 50, 60, 91) varies in accordance with the relative position of the contact portion (10m, 50m, 60m, 91m) and the contacted portion (40m, 70m) in the circumferential direction that is around the insertion direction of the post into the aperture (P40, P70), the extent of the expansion of the aperture (P40, P70) allowed by the second member (10, 50, 60, 91) being adjustable in accordance with the rotation of one of the first member (40, 70) and the second member (10, 50, 60, 91) relative to the other, characterized in that when the contact portion (10m, 50m, 60m, 91m) and the contacted portion (40m, 70m) face one another, the post which has been inserted through the aperture (P40, P70) is prohibited from disengaging from the female snap button, and when the contact portion (10m, 50m, 60m, 91m) and the contacted portion (40m, 70m) do not face one another, the post which has been inserted through the aperture (P40, P70) is not prohibited from disengaging from the female snap button.