A fluid machine with radial cylinders, includes cylinders being fixed with respect to a body wherein the cylinders are peripherally spaced in a rotation plane of a crank rotating with a driving shaft of the machine, elements distributing a fluid, a piston of each cylinder placed in contact with a surface of the crank by a sliding member, the piston of each cylinder being placed within a jacket of the cylinder with contact of a side surface of the piston in a guide and sealing area which is small with respect to the side surface of the piston, and for a guide function an annular edge is present and projecting from an inner surface of the jacket, and for a sealing function a sealing ring is present on the jacket and housed in an annular slot which is parallel and attached to the annular edge, and rings maintaining the contact between the pistons and the crank.