To provide a rivet pressing device which can rapidly and easily perform attachment to and detachment from a car body frame of a motor truck, can surely press-hold the rivet even during striking work, and has excellent compatibility with car body frames having different sizes.

A hydraulic long ram 1, a variable extension 2, an extension tube 3, a lock-on adapter 4, a pressure sensing member 5, two types of rivet pressing tools 6, 7, a hydraulic short ram 8, an extension base 9, three types of extensions 10, 11, 12, two bolts 13 for fixing the extension base 9 and other constituent members are combined to provide a rivet pressing device, which can be disposed horizontally between side members constituting a car body frame of a motor truck, or a rivet pressing device which can be disposed vertically within the side members.