A disposable diaper includes side flaps； pieces of fastening tape respectively arranged on widthwise side portions of the side flaps； and joining portions each of which joins a portion of each piece of the fastening tape to a non-skin side of the side flaps in the thickness direction. In an unfolded state, for each of the pieces of fastening tape, a magnitude of force applied at a time when the joining portion is peeled off when a region of the fastening tape that is outward in the width direction with respect to the joining portion is pulled in an outward direction is greater than a minimum value of an magnitude of force applied at a time when the joining portion is peeled off when a region of the fastening tape that is inward with respect to the joining portion is pulled in any outward direction.
