A fluid transfer device comprising: first and second tanks (13, 14) each configured to store a fluid containing fine powder; a communication pipe through which the first and second tanks (13, 14) communicate with each other; and a transfer portion configured to transfer the fluid stored in the first tank (13 (or 14)) to the second tank (14 (or 13)) and transfer the fluid stored in the second tank (14 (or 13)) to the first tank (13 (or 14)), characterized in that: each of the first and second tanks (13, 14) includes a first chamber and a second chamber that are separated by a deformable dividing wall; each of the first chambers stores an incompressible fluid; each of the second chambers stores the fluid having higher specific gravity and viscosity than the incompressible fluid; the second chambers of the first and second tanks (13, 14) communicate with each other through the communication pipe; when the transfer portion supplies the incompressible fluid to the first chamber of the first tank (13 (or 14)), (i) the volume of the incompressible fluid in the first chamber of the first tank (13 (or 14)) increases, (ii) the dividing wall of the first tank (13 (or 14)) deforms to move from the first chamber side to the second chamber side, (iii) the volume of the second chamber of the first tank (13 (or 14)) decreases, (iv) the fluid stored in the second chamber of the first tank (13 (or 14)) is transferred through the communication pipe to the second chamber of the second tank (14 (or 13)), (v) the volume of the fluid in the second chamber of the second tank (14 (or 13)) increases, (vi) the dividing wall of the second tank (14 (or 13)) deforms to move from the second chamber side to the first chamber side, (vii) the volume of the first chamber of the second tank (14 (or 13)) decreases, and (viii), the incompressible fluid is discharged from the first chamber of the second tank (14 (or 13)); and a stirring device configured to stir the fluid in the communication pipe is provided on the communication pipe. first and second tanks (13, 14) each configured to store a fluid containing fine powder; a communication pipe through which the first and second tanks (13, 14) communicate with each other; and a transfer portion configured to transfer the fluid stored in the first tank (13 (or 14)) to the second tank (14 (or 13)) and transfer the fluid stored in the second tank (14 (or 13)) to the first tank (13 (or 14)), characterized in that: each of the first and second tanks (13, 14) includes a first chamber and a second chamber that are separated by a deformable dividing wall; each of the first chambers stores an incompressible fluid; each of the second chambers stores the fluid having higher specific gravity and viscosity than the incompressible fluid; the second chambers of the first and second tanks (13, 14) communicate with each other through the communication pipe; when the transfer portion supplies the incompressible fluid to the first chamber of the first tank (13 (or 14)), (i) the volume of the incompressible fluid in the first chamber of the first tank (13 (or 14)) increases, (ii) the dividing wall of the first tank (13 (or 14)) deforms to move from the first chamber side to the second chamber side, (iii) the volume of the second chamber of the first tank (13 (or 14)) decreases, (iv) the fluid stored in the second chamber of the first tank (13 (or 14)) is transferred through the communication pipe to the second chamber of the second tank (14 (or 13)), (v) the volume of the fluid in the second chamber of the second tank (14 (or 13)) increases, (vi) the dividing wall of the second tank (14 (or 13)) deforms to move from the second chamber side to the first chamber side, (vii) the volume of the first chamber of the second tank (14 (or 13)) decreases, and (viii), the incompressible fluid is discharged from the first chamber of the second tank (14 (or 13)); and a stirring device configured to stir the fluid in the communication pipe is provided on the communication pipe. each of the first and second tanks (13, 14) includes a first chamber and a second chamber that are separated by a deformable dividing wall; each of the first chambers stores an incompressible fluid; each of the second chambers stores the fluid having higher specific gravity and viscosity than the incompressible fluid; the second chambers of the first and second tanks (13, 14) communicate with each other through the communication pipe; when the transfer portion supplies the incompressible fluid to the first chamber of the first tank (13 (or 14)), (i) the volume of the incompressible fluid in the first chamber of the first tank (13 (or 14)) increases, (ii) the dividing wall of the first tank (13 (or 14)) deforms to move from the first chamber side to the second chamber side, (iii) the volume of the second chamber of the first tank (13 (or 14)) decreases, (iv) the fluid stored in the second chamber of the first tank (13 (or 14)) is transferred through the communication pipe to the second chamber of the second tank (14 (or 13)), (v) the volume of the fluid in the second chamber of the second tank (14 (or 13)) increases, (vi) the dividing wall of the second tank (14 (or 13)) deforms to move from the second chamber side to the first chamber side, (vii) the volume of the first chamber of the second tank (14 (or 13)) decreases, and (viii), the incompressible fluid is discharged from the first chamber of the second tank (14 (or 13)); and a stirring device configured to stir the fluid in the communication pipe is provided on the communication pipe.