PURPOSE: To easily adjust the tension of a chain by supporting a tension adjusting screw with a bearing on a casing portion loosely connected to a saw main body.

CONSTITUTION: The saw-blade 15 of a chain saw is fixed to a saw main body by blade bolts, and the saw blade 15 can be displaced in the longitudinal direction by a tension adjusting screw 24 and dogs 19, 20 arranged in the longitudinal direction. The dogs 19, 20 connected to the saw blade 15 and the tension adjusting screw 24 are arranged in the cavity 18 of the saw main body. The tension adjusting screw 24 is supported by a bearing on a casing portion 10 loosely connected to the saw main body. When the tension adjusting screw 24 is rotated, the position adjustment of the saw blade 15 and the tension adjustment of a chain can be made.