To form a U-shaped cross-section cover with high bonding strength, which causes little distortion.

This cover device comprises a sheet-metal cover body 4 for covering the top surface, front surface, right and left side surfaces of a structure 3 on a revolving frame 2, and a cap body 5 which is provided on the top surface of the cover body 4. In the cover body 4, a left split material 4L, which is obtained by integrally molding a half top surface portion A, a half front surface portion B and a left side surface portion L together, and a right split material 4R, which is obtained by integrally molding the half top surface portion A, the half front surface portion B and a right side surface portion R together, are joined together via a split surface P. In the right and left split materials 4R and 4L, the half top surface portion A is joined via upward protruding flanges 6a and 6b; the half front surface portion B is joined via overlap edges 7a and 7b which overlap each other on the inside and the outside; and an opening 8 is formed between a flange joint 6 and an overlap joint 7.