To obtain a necessary amount of mortar in a narrow site by loading a mixer with a material loading chamber provided with a transfer means for transferring mortar material from an agitating chamber to a loading chamber to be moved.

Sand, cement, an additive and the like are metered and discharged to a mixing chamber by a screw conveyors 11, 31 at a prescribed ratio, made homogenous by rotating and mixing of a rotating plate, and discharged to the agitating chamber. Next, water supply is received from a nozzle, they are kneaded by a moving blade, discharged as mortar, and transferred by a wheel barrow (i) or a mortar discharge pump to a necessary part. At the time, a part of a mixer is transferred to the rear side of the load-carrying platform of a truck (t), a discharging opening 4a is protruded rearward of the load-carrying platform, the wheel barrow (i) is put on the rear part of the load-carrying platform, and mortar from the discharge opening 4a is directly received. After completion of mortar working, a hose from a water source is removed, and the truck can move. Thereby exclusive use of a large area is made unnecessary, at the time of need, a necessary amount of mortar can be produced and supplied to a site.