To provide a lightweight interlocking mat substituted for a conventional heavy tatami mat and mutually connected to each other without forming a clearance between mats.

This interlocking mat 7 comprises a plurality of projecting pieces 2 provided around the circumferential edges of a square resin foam plate at same intervals, a base 1 formed with curved parts 3 between the projecting pieces 2 having a shape for fitting in the projecting pieces 2, a tatami facing 4 covering the surface of the square resin foam plate, a tatami hem 5 attached thereto, or without the tatami hem, and a cover part 6 having such a dimension that, when adjoining two sides are accorded and stacked with the tip edges of the projecting pieces 2 of the adjoining two sides of the base 1, the residual two sides are accorded with the deep line of the curved parts 3 of the base 1 and the projecting pieces 2 project from the residual adjoining two sides. This interlocking mat 7 is so formed that the adjoining two sides of the cover part 6 are stacked and accorded with the tip edge of the projecting pieces 2 of the adjoining two sides of the base 1, and the base 1 and the cover part 6 are joined with each other.