To provide a cutting device for a straight member, which easily cuts the straight member without breaking it, and also carries out cutting in accurate dimensions, in regard to a cutting device rotating a rotary cutter at a high speed to cut a straight member such as a wiring duct.

The cutting device K for a straight member is provided with the rotary cutter 2 for cutting a straight member W such as a duct, and a work mounting table 34 for mounting the straight member, freely slidable in directions approaching and separating away from the rotary cutter. It is composed such that the work mounting table 34 is provided with: a first positioning means S1 for abutting on the mounted straight member to define a cutting length; and a second positioning means S2 for defining a length from a cutting part of an attachment elongate hole of a bottom part provided in the straight member.