A mortiser or morticer is a specialized woodworking machine used to cut square or rectangular holes in a piece of lumber, such as a mortise in a mortise and tenon joint.

The square chisel mortiser (also called hollow chisel mortiser), similar to a drill press in many respects, combines the cutting of a four-sided chisel with the action of a drill bit in the center. The bit clears out most of the material to be removed, and the chisel ensures the edges are straight and clean.

Square chisel mortising bits can also be fitted to normal drill presses using a mortising attachment.

This device was invented in 1874 by Robert and Ralph Greenlee