An eye examining instrument comprises an ultrasonic wave generating source, reflecting members and a receiver. A concave reflecting mirror is provided to direct the generated ultrasonic waves in the direction along the optical axis of the objective lens of the instrument while converging the waves. Also, a concave reflecting mirror is provided to converge the ultrasonic waves reflected upon the cornea of the eye under test and examination into the receiver. The ultrasonic waves received by the receiver are transformed into an electric signal. The electric signal thus produced includes a component informing of the time required to receive the ultrasonic waves after the generation thereof and a component informing of the intensity of the received ultrasonic waves. The time component signal is compared with a reference signal representative of a predetermined working distance between the objective lens and the eye whereas the intensity component signal is compared with a reference signal representative of the alignment of the objective lens with the eye.