To provide a cutting tool for a channel member capable of simply and easily cutting the channel.

The cutting tool for cutting the channel member 10 composed of both side plate parts (a) and (b) and a bottom plate part c is composed of a first clamping rod 1 with a U-shaped cutting blade 3 formed so as to be externally fitted from the outer surface side of the bottom plate part c to the channel 10 on a distal end side, a second clamping rod 2 with a trapezoidal cutting blade 4 facing the U-shaped cutting blade 3 of the first clamping rod 1 on the end side, and holding rods 5 and 6 for opening/closing operations respectively connected to the respective rear end parts of both clamping rods 1 and 2. The first clamping rod 1 and the second clamping rod 2 are pivotally attached by a pivot 7 such that the U-shaped cutting blade 3 and the trapezoidal cutting blade 4 are mutually opened and closed, both cutting blades 3 and 4 are closed while being successively overlapped from the tip side cutting blade part to the front side cutting blade part when they are closed, and both cutting blades 3 and 4 are opened while being separated successively from the front side cutting blade part to the tip side cutting blade part when they are opened.