To provide a compact and low-cost work machine in which aligning between a cutting tool and a guide bush is not required, and in which the cutting tool and the guide bush can be easily changed.

A tool holder 22 provided with a cutting tool 20 is detachably installed on a first movable device, and a chuck for holding a guide bush 24 is installed on a second movable device. A pawl 34 is formed in the tool holder 22, a groove to be engaged with the pawl 34 is formed in the guide bush 24, and a spring 58 for holding the pawl 34 in the groove is provided. The guide bush 24 is engaged with the cutting tool 20, the groove in the guide bush 24 is engaged with the pawl 34 of the tool holder 22, and their engagement condition is held by the spring 58. The guide bush 24 and the cutting tool 20 are thus attached to/detached from this drilling work machine as combined with the tool holder 22.