This paper describes a modification of an automatic liquid manometer on the basis of a position-detecting system that has been reported in our previous papers. It operates as follows. A laser beam is reflected by the meniscus of liquid in a glass tube manometer and a spot of light is created on a screen which is put on the outer side of the glass tube. The position of the meniscus can be known by detecting the spot of light through a position sensitive detector (PSD). An application of external pressure to the manometer moves the position of the meniscus. The vertical displacement of the reservoir required to return the meniscus to its original position is equal to the pressure head that is applied to the manometer. In this paper the influences of the inclination angle of glass tube and the incidence angle of laser beam on the characteristics of the system are discussed and their optimum combinations are determined.