An apparatus for monitoring a bloodstream in a skin surface including a laser light source for emitting a laser beam, a cylindrical lens for expanding the laser beam, an objective lens for collecting light rays reflected by the skin surface and scattered by blood cells, a linear image sensor for receiving the reflected light rays via an objective lens, A/D converter for converting output signals read out of light receiving elements of the linear image sensor into digital signals, a memory for storing the digital signals, a calculating circuit for calculating a bloodstream velocity or a distribution of bloodstream, and a display device for displaying the bloodstream velocity or the distribution of bloodstream.