A pointing device, a keyboard assembly, and a portable computer are disclosed. The pointing device can be minimized and has an excellent performance on resisting impact. The pointing device includes an operation cap having an operation surface fitted into a stud. The stud is fixed to a keyboard plate with a screw from below together with a sensor plate. A waterproof material is provided between the stud and the keyboard plate. Multiple pressure sensors are arranged below the keyboard plate. The pressure sensors are applied with a predetermined pressure beforehand. When the operation surface is depressed, the stud and the sensor plate slide and move downward while being tilted to reduce the detection pressures of the pressure sensors. Since the pressure sensors exist below the keyboard plate, the operation cap can be downsized, and the pressure sensors can be protected from impact to the operation cap.