To provide a mortar injection device which prevents an air bubble from being mixed in mortar when discharging the mortar by air pressure, and is capable of continuously discharging the mortar.

A mortar injection device comprises: a pressure cylinder 2 which is capable of casting mortar; a pressure piston 4 which contacts a surface of the mortar cast by the pressure cylinder 2; a pressure valve 33 which can be connected to a compressor 6 for compressing the pressure piston 4 by pressing force of air; and discharge ports 51 to 54 which discharge the mortar pressed by the pressure piston 4. As the discharge ports, a plurality of the discharge ports 51 to 54 with an identical diameter are installed in the mortar injection device so that the mortar is discharged through one of the discharge ports and continuously supplied through another discharge port which is connected to a mortar supply device 7.