A chain saw comprising a guide bar,an arrangement for transferring fluid to the guide bar, at least a power unit, a chain sprocket driven by the power unit, and a saw chain to be rotated along the guide bar thereof, wherein the guide bar comprises a fastening arrangement with which it is rotatably fastened to a body of the chain saw, wherein a tensioning device is arranged to act on the guide bar fastening arrangement, whereby it causes in the guide bar a distancing movement in relation to the chain sprocket in the direction of the longitudinal axis of the guide bar for tensioning the saw chain, wherein said tensioning device comprises at least one transfer member arranged to the chain saw body and causing the movement substantially in the direction of the longitudinal axis of the guide bar, the transfer member being in contact with a counter surface on the guide bar or in the fastening arrangement thereof, and the fastening arrangement of the guide bar and the chain saw body are joined by at least one support guide (10a, 10b) to provide the movement of said guide bar in the direction of the longitudinal axis thereof, characterized in that the arrangement further comprises a channel means extending from the chain saw body to the fastening arrangement so that the direction of the longitudinal axis of the channel means is substantially in the direction of influence of the transfer member, and the channel means comprises a cavity through the entire means, and a first end of said channel means is connected to a feed channel provided in the chain saw body, and a second end of the channel means is connected to a counter channel provided in the fastening arrangement, the counter channel being arranged to extend into connection with the guide bar, whereby the channel means is slidingly arranged by the ends (17, 18) thereof either to the feed channel in the chain saw body or the opposite counter channel in the fastening arrangement, and the channel means is arranged to guide fluid flowing in the feed channel provided in the chain saw body through the channel means and further to the guide bar through the counter channel provided in the fastening arrangement. the guide bar comprises a fastening arrangement with which it is rotatably fastened to a body of the chain saw, wherein a tensioning device is arranged to act on the guide bar fastening arrangement, whereby it causes in the guide bar a distancing movement in relation to the chain sprocket in the direction of the longitudinal axis of the guide bar for tensioning the saw chain, wherein said tensioning device comprises at least one transfer member arranged to the chain saw body and causing the movement substantially in the direction of the longitudinal axis of the guide bar, the transfer member being in contact with a counter surface on the guide bar or in the fastening arrangement thereof, and the fastening arrangement of the guide bar and the chain saw body are joined by at least one support guide (10a, 10b) to provide the movement of said guide bar in the direction of the longitudinal axis thereof, characterized in that the arrangement further comprises a channel means extending from the chain saw body to the fastening arrangement so that the direction of the longitudinal axis of the channel means is substantially in the direction of influence of the transfer member, and the channel means comprises a cavity through the entire means, and a first end of said channel means is connected to a feed channel provided in the chain saw body, and a second end of the channel means is connected to a counter channel provided in the fastening arrangement, the counter channel being arranged to extend into connection with the guide bar, whereby the channel means is slidingly arranged by the ends (17, 18) thereof either to the feed channel in the chain saw body or the opposite counter channel in the fastening arrangement, and the channel means is arranged to guide fluid flowing in the feed channel provided in the chain saw body through the channel means and further to the guide bar through the counter channel provided in the fastening arrangement.