PURPOSE: To perform underwater cleaning work reliably by providing cylindrical floats having variable air volume in front and rear of the impeller of an outerboard cleaning machine to be mounted on an adsorption travel truck and making the floating force of cleaning machine regulatable.

CONSTITUTION: In a cleaning machine to press against an underwater outerboard through rotation of impeller thus to remove ocean livings adhered onto the surface by means of a cleaning brush, cylindrical floats 30, 31 are provided symmetrically in front and rear or to the left and right of an impeller 1A. The volume of air chamber in said floats 30, 31 is made variable by controlling the supply of air through an air transmission tube 32 thus to regulate the floating force of floats 30, 31. Various floating force of sea water or pure water can be regulated effectively through said floats 30, 31 resulting in reliable and efficient cleaning work under the water.