To improve the strength to chattering or deflection in a boring bar having a cemented carbide guide pad and a reinforcement on the circumference of a bar by integrally constituting the guide pad and the reinforcement in such a manner that the tip side of a cemented carbide strip material forms the guide pad, and the rear end side thereof forms the reinforcement.

In this boring bar 1 suitable for deep hole boring, a cartridge 5 for attachably and detachably clamping a cutting edge tip 4 is mounted at the tip part, an axial groove is provided on the circumferential part of the bar, and a cemented carbide strip 6 is buried in this groove and brazed thereto. For example, three strips 6 are mounted circumferentially, the base end side of one strip 6 is formed substantially in the same diameter as the outer diameter of the bar as a reinforcement 3. The tip side of the strip 6 is formed as a guide pad 2. According to this, the guide pad 2 charges the role as the reinforcement, and the strengthened reinforcement 3 and the guide pad 2 effectively work to prevent the chattering or deflection.