To provide a sheet binding device binding a sheaf of sheets by pressurizing it with a pair of crimping tooth having concave-convex shape, in which the binding force for binding the sheet sheaf may be enhanced with a smaller increment of pressure than conventional means.

A sheet binding device, such as an end part binding part 25, is so constructed that a sheaf of sheet Pb is pressurized and bound with a pair of upper crimping teeth 101 and lower crimping teeth 102 having concave-convex shape. In addition, on the end part in the pressurizing direction of the upper crimping teeth 101 and the lower crimping teeth 102, a plane surface part 101c and a plane surface part 102c which have an approximately parallel surface facing the surface of the sheet sheaf Pb to be bound are arranged so that they face each other. In addition, in an approximately vertical direction relative to the surface of the sheet sheaf Pb, a pressurization mechanism 110a moving the upper crimping teeth 101 and a slide mechanism 120 moving the lower crimping teeth 102 in the teeth width direction parallel with the sheet surface of the sheet sheaf Pb are arranged.