To provide a flap clasp for a bag such as a school satchel adjusting a fixing position on a female member side and automatically rotating an operating tab.

The flap clasp 5 includes means for adjusting the fixing position on the female member side on at least three stages, and means for automatically turning the operating tab 63. (A) In the means for adjusting the fixing position on the female member side on at least three stages, an engagement projection can be selectively engaged with a slit. (B) The means for automatically turning the operating tab is formed of a rotary plate 8 attached to the operating tab 63, a spring for urging the rotary plate with turning force, (b) a clasp for limiting the range of turning of the rotary plate, and means for turning the rotary plate by the contact with the female member.