An ophthalmic ultrasonic diagnostic apparatus for measuring a length of a constituent part of an examinee's eye by A-mode measurement, the apparatus comprising: an ultrasonic probe for A-mode measurement including a transducer for emitting ultrasonic waves into the examinee's eye and receiving echoes reflected from the constituent part; a sampling memory for storing waveform signals of the echoes received by the transducer; calculation means for judging whether the stored echo's waveform signals are appropriate and calculating measurement values of the length of the constituent part based on the echo's waveform signals which are judged as appropriate; and a memory for storing the calculated measurement values, characterized in that the ophthalmic ultrasonic diagnostic apparatus further comprises: grouping means for setting a plurality of grouping ranges (Dn, En, Gn) having a predetermined permissible dispersion range (ΔD) for grouping the measurement values into a plurality of groups, the grouping means being arranged to perform either one of: (a) setting the plurality of grouping ranges by setting, at every obtainment of a new measurement value, a grouping range having a permissible dispersion range with reference to the newly obtained measurement value; (b) setting the plurality of grouping ranges in steps of a predetermined width (Δd) in a range including the lowest and highest measurement values stored in the memory; (c) setting the plurality of grouping ranges in steps of a predetermined width (Δd) with reference to the measurement value which is obtained first; and (d) setting the plurality of grouping ranges based on a known range of the axial length of a human eye, and in that the calculation means is arranged to count for each set grouping range a number (Nn) of the measurement values which fall within the respective grouping range, determine the measurement values that fall within the one grouping range of the plurality of grouping ranges whose number (Nn) is largest as effective data, and calculate an average value of the measurement values that fall within the one grouping range, wherein the measurement is automatically stopped when the number (Nn) equals a predetermined value (Np). an ultrasonic probe for A-mode measurement including a transducer for emitting ultrasonic waves into the examinee's eye and receiving echoes reflected from the constituent part; a sampling memory for storing waveform signals of the echoes received by the transducer; calculation means for judging whether the stored echo's waveform signals are appropriate and calculating measurement values of the length of the constituent part based on the echo's waveform signals which are judged as appropriate; and a memory for storing the calculated measurement values, characterized in that the ophthalmic ultrasonic diagnostic apparatus further comprises: grouping means for setting a plurality of grouping ranges (Dn, En, Gn) having a predetermined permissible dispersion range (ΔD) for grouping the measurement values into a plurality of groups, the grouping means being arranged to perform either one of: (a) setting the plurality of grouping ranges by setting, at every obtainment of a new measurement value, a grouping range having a permissible dispersion range with reference to the newly obtained measurement value; (b) setting the plurality of grouping ranges in steps of a predetermined width (Δd) in a range including the lowest and highest measurement values stored in the memory; (c) setting the plurality of grouping ranges in steps of a predetermined width (Δd) with reference to the measurement value which is obtained first; and (d) setting the plurality of grouping ranges based on a known range of the axial length of a human eye, and (a) setting the plurality of grouping ranges by setting, at every obtainment of a new measurement value, a grouping range having a permissible dispersion range with reference to the newly obtained measurement value; (b) setting the plurality of grouping ranges in steps of a predetermined width (Δd) in a range including the lowest and highest measurement values stored in the memory; (c) setting the plurality of grouping ranges in steps of a predetermined width (Δd) with reference to the measurement value which is obtained first; and (d) setting the plurality of grouping ranges based on a known range of the axial length of a human eye, and