To provide a roof material cutter which is lightweight and compact, can be carried, and can cut roof materials into various thicknesses and shapes without scattering cut dust.

The roof material cutter includes a back-and-forth movable girder 3 holding a vertically movable cutter mechanism 2 and capable of traveling back and forth, a traveling girder stand 4 for holding both ends of the movable girder, a cutter groove 2 for traveling a cutting rotary blade on a cutting table, and a cutting stopper for determining a cutting position. The roof material is placed on the cutting table 1 having a structure to prevent the dust from being scattered. Then, while rotating the rotary blade of the cutter mechanism 2, the cutter mechanism 2 moving vertically in accordance with the shape of the roof is traveled along the cutter groove, so as to cut the roof material.