To provide lightweight mortar which suppresses the change in flowability with time until setting starts even after pouring water and kneading, in cement-based lightweight mortar using lightweight aggregate and super lightweight aggregate as fine aggregate, and which, for example, can develop flowability having no trouble on filling operation, irrespective of the elapsed time from the pouring-water and kneading, irrespective of the presence of a thickening component, and without affecting the curability.

The lightweight premixed mortar includes cement and lightweight fine aggregate having a speed of water absorption per unit volume one minute after pouring water from an absolute dry condition of 500-900 kg/min. The lightweight premixed mortar preferably includes lightweight fine aggregate having a weight per unit volume of 0.5 kg/l or less.