Abstract: A transilluminator device for locating blood vessels in the tissue. The device includes a plurality of the light emitting diodes with appropriate wavelength. The light emitting diodes emit light through the tissue being examined. This transilluminator device applies the light emitting diodes to emit light into tissue, using the difference of light absorption spectra between tissue and blood vessels to enhence color contrast for locating blood vessels in the tissue. A light intensity adjusting mechanism is intergrated into the transilluminator device to provide the optimal effect individually. The transilluminator device provides the sensors to assure that the light emitting diodes are enabled only when it is in good contact with patient's skin to prevent the physician's eyes from harsh light. The transilluminator device includes a plurality of hook on the basal surface. The hooks comprise a plurality of indentation or a plurality of flange.