We have proposed a novel method of Schlieren imaging, a simple Schlieren method, by which acoustic fields of medical ultrasound equipment are visualized without using a conventional large and expensive Schlieren optical system. In this study, we used a newly developed system that was constructed using relatively low-cost components: a short-pulsed laser diode of 50 ns in pulse width and 20 W in optical power as a light source, a consumer digital camera of 12-bit A/D without a cooling system as an imaging device, and a personal computer as an image processor for generation of a Schlieren image using a pair of images taken in the presence and absence of ultrasound pulse in an observing field. Use of the short-pulsed laser diode enables observation of instantaneous acoustic fields of a traveling ultrasound pulse. Acoustic fields of a diagnostic ultrasound transducer were visualized using the newly developed system, and Schlieren images showed good agreement with acoustic fields measured using a membrane hydrophone. Tomographic reconstruction of a 3-D acoustic field was also carried out using a filter backprojection algorithm. Eight Schlieren images observed at different directions were used for the reconstruction, and the results showed the usefulness of the proposed Schlieren method for tomographic reconstruction.