To provide a stretchable inner waist belt capable of finely tightening the waist line of a wearer and also keeping appearance excellent without generating e.g. creases, twist around a belt part even if the belt is tightened from on the belt part of a clothing.

This stretchable inner waist belt 1 is detachably attached to the reverse side (inner side) of a pair of trousers 15 having a waist size adjustment mechanism with snaps 7. A wearer puts on the pair of trousers 15 and fixes the Hook-and-Loop fastener 4 of the stretchable inner waist belt 1 to a place in a desirably tightened condition, and when the wearer adjusts the waist size of the pair of the trousers 15 so as to fit to the tightened waist size, with a hooking metal fitting composed of a hook 17 with two hook parts and a receiving eye 18 with two receiving parts, the pair of trousers 15 tightly fits to the waist size of the wearer and appearance can be kept excellent without generating e.g. creases, twist around a belt part 16.