To easily fill mortar into a joint clearance without fouling the hands and without needing to worry too much about the kneaded degree of mortar and to allow mortar to be pressed with a joint trowel immediately after filled.

The joint trowel comprises a container 1 for filling mortar, and a trowel 2 for pushing out the mortar in the container. The trowel 2 is provided in a reciprocating manner to the container 1. The container is formed to use the whole area of one face of a filling box 3 of bottomed cylinder shape as a discharge port 4 of mortar, to form the filling box 3 in conformity to the joint clearance and to bore a guide hole 10 in an opposite face to the discharge port 4 of the filling box 3 to reciprocate the trowel. The trowel 2 has a push-out rod 13 to pass through the guide hole 10, and a trowel plate 12 at the tip part of the push-out rod 13 to push out the mortar in the filling box 3 at a stroke. The trowel plate 12 can be put in and out of the filling box 3 from the discharge port 4 following the motion of the push-out rod 13.