To expand a detection range of an automatic alignment and a detection range for access prevention with a simple structure.

In an alignment detecting optical system, the wavelength alone of a light source 43 passes through split prisms 35a and 35b, a luminous flux is refracted upward by the left prism 35a and downward by the right prism 35b so that a spot image of the light source 43 is formed as two calescence points arrayed vertically near the center on an image sensor 37. As positional deviation of the two calescence points is detected, a longitudinal drive motor 5, a vertical drive motor 12 and a horizontal drive motor are driven to automatically adjust a tonometry part 1 to the optimum alignment position by a feedback control. As eyes to be examined approach the tip of a nozzle 31 to make an imaging detecting surface dark as a whole covering an observation range, the tonometry part 1 is retreated backward and when a pupil part and an alignment calescence point of the eyes E to be examined are detected again, an automatic alignment is continued to accomplish a tonometry.