To provide a guide apparatus which is usable for linearly moving an electric circular saw, able to be easily carried and installed and to reduce roughness of cut surface, and also has a simplified configuration.

A guide apparatus with an electric circular saw 51 on which a saw blade 52 for cutting a workpiece W can be mounted is composed of: a base plate 11 coming into contact with the workpiece W; guide means 12 extending along the base plate 11; a guide block 17 movable along the guide means 12; and a support device 31 attached to the guide block 17. Further, a fulcrum shaft 57 and a projection piece 60 are assembled into the electric circular saw 51. An upright plate 32 having a side groove 36 which receives the fulcrum shaft 57, and a restriction plate 34 for preventing the projection piece 60 from floating are provided at the support device 31. Change of attitude of the electric circular saw 51 is suppresses by the restriction plate 34, whereby roughness of cut surface can be prevented. Further, by use of only one guide block 17, the width of the base plate 11 can be suppressed, whereby transportation and so on of the guide apparatus can be easily performed.