A viscous material supply device comprising: a tank provided with a storage space storing viscous material; a piston slidably inserted into the tank, and is provided with a pressing surface that presses the viscous material and a suction passage through which the viscous material inside the tank flows by pressing force of the pressing surface; a covering sheet including a covering part covering the pressing surface in the piston and a communication hole communicating with the suction passage; a sealing member attached to an outer periphery of the piston and sealing a portion between the piston and the tank; characterized by covering sheet comprising a folded back portion (f1, f3) at which the covering sheet is folded back at an outer periphery towards a side of the piston opposite to the pressing surface, wherein the folded back portion includes insertion holes; and pins erected on the side opposite to the pressing surface in the piston, wherein the insertion holes of the covering sheet are fitted with the pins to attach the covering sheet to the piston; wherein the insertion holes are fitted with the pins and wherein axis centers of the suction passage and the communication hole are matched with each other; the piston further includes a first outer shape part on which the sealing member is attached and a second outer shape part separated from the first outer shape part in a direction that the piston slides and whose outer periphery is formed larger than the first outer shape part, and the sealing member has an outside surface positioned further outward in a radial direction than the covering sheet attached to the piston, at least in the first outer shape part. a tank provided with a storage space storing viscous material; a piston slidably inserted into the tank, and is provided with a pressing surface that presses the viscous material and a suction passage through which the viscous material inside the tank flows by pressing force of the pressing surface; a covering sheet including a covering part covering the pressing surface in the piston and a communication hole communicating with the suction passage; a sealing member attached to an outer periphery of the piston and sealing a portion between the piston and the tank; characterized by covering sheet comprising a folded back portion (f1, f3) at which the covering sheet is folded back at an outer periphery towards a side of the piston opposite to the pressing surface, wherein the folded back portion includes insertion holes; and pins erected on the side opposite to the pressing surface in the piston, wherein the insertion holes of the covering sheet are fitted with the pins to attach the covering sheet to the piston; wherein the insertion holes are fitted with the pins and wherein axis centers of the suction passage and the communication hole are matched with each other; the piston further includes a first outer shape part on which the sealing member is attached and a second outer shape part separated from the first outer shape part in a direction that the piston slides and whose outer periphery is formed larger than the first outer shape part, and the sealing member has an outside surface positioned further outward in a radial direction than the covering sheet attached to the piston, at least in the first outer shape part.