To provide a reamer which can change set-in machining tool simply and quickly and in which the fastening force to the tool is dispersed over a wide area.

A reamer 10 includes a retainer 11 and a number of set-in type machining tools 12, and the retainer 11 is furnished with a number of pockets 22, wherein the machining tools 12 are installed in line substantially and a protrusion is formed which is incremental continuously from the retainer 11. The reamer 10 is equipped with fastening means for respective machining tools 12, and there spring-loaded clamps 15 are installed to press each machining tool 12 to the supporting surface 21 of respective pocket.