To provide a line boring machine capable of adjusting automatically the protrusion amount of a tool for a line bar.

A work clamping mechanism 14 is installed through a pedestal 13 of a machine base frame 1, and on a supporting frame 21, a line bar holding mechanism 44 for holding a line bar 12 in the adjust position P1 is installed. Also on the supporting frame 21, a tool protrusion amount adjusting device 81 is installed for adjusting the protrusion amount of the tool 52 of the line bar 12 held by the holding mechanism 44. A Z-axis saddle 84 of the tool protrusion amount adjusting device 81 is moved in the Z-axis direction while a Y-axis saddle 93 is moved in the Y-axis direction so that a clamping claw 103 is positioned mating with the tool 52 of the line bar 12. An adjusting nut 55 of the tool 52 is clamped by the claw 103 and the claw is revolved by a revolving mechanism 102, and thereby the adjusting nut 55 is rotated to adjust the protrusion amount of the tool 52 automatically.