To provide a booster for a washer capable of simply connecting an air exhausting cylinder and a booster.

Concerning this booster, the washer and a table 7 are arranged along the wall surface 1 of a building, the booster 9 is disposed adjacently to the washing machine in a space under this table 7 and the air exhausting cylinder 11 of this booster 9 is extended over the table 7 along the surface 1. In this case, an air exhausting cylinder supporting plate 21 to be extended to the back surface part of the booster is disposed on the back surface part of the cylinder 11 and an air exhausting cylinder supporting board receiving plate 23 inserting-holding this plate 21 is disposed on the back surface part to fix the front surface part of the cylinder 11 to the booster 9.