Recently, transducers with high resolution are required in the fields of ultrasonic imaging and non-destructive testing. The plano-convex and plano-concave transducers treated in this paper are suitable for these purposes. These transducers show the focusing effect and broad frequency bandwidth for the radiation of ultrasonic pulses. These two features show the high lateral-distance and time resolutions respectively. However, the principle of the focusing effect on these transducers has been vague until now. This focusing effect will be discussed in this paper. The mechanisms of the focusing effect for ultrasonic pulses radiated from the plano-convex and plano-concave transducers are cleared through two experiments using a wedged transducer and a semi-cylindrical transducer. Also, the formulas for the geometrical focal points of pulses radiated from each transducer are derived, and its calculations are compared with the measurements.