A sheet binding device includes a binding operation unit including a first tooth-shaped member that has plural arrayed teeth, a second tooth-shaped member that has plural arrayed teeth and binds sheets by biting the first tooth-shaped member to clamp the sheets in cooperation with the first tooth-shaped member, and a link structure that opens and closes the first tooth-shaped member and the second tooth-shaped member to perform a binding operation, and two side frames that are arranged to hold the binding operation unit therebetween and to support the binding operation unit on both sides of the binding operation unit.