To provide a form for jointing slab concrete facilitating mounting and dismantling of the form provided in a concrete jointing part, enabling adjustments of width according to the spacing between slab reinforcements which differs with construction sites, and making the form usable for other purposes, when the slab concrete of a concrete building is placed as it is divided for a plurality of construction areas.

The jointing form blocks the jointed parts of slab concrete by adjusting the overlap width of a first sheathing board 2 and a second sheathing board 3 which are erected between the slab reinforcements. Recesses 6 (6a, 6b) for locking half of each slab reinforcement according to the height of the slab reinforcement are formed in one vertical side of each sheathing board where the first sheathing board 2 and the second sheathing board 3 partially overlap. Guide holes 7 for passing fixing rods 8 therethrough are provided on both sides of the first sheathing board 2 along the vertical direction and on one side of the second sheathing board 3 along the vertical direction. A driving part 11 provided at the lower end of the fixing rod 8 passed through the guide hole 7 is driven into the slab form to fix the first sheathing board 2 and the second sheathing board 3 together.