An intravascular diagnostic or therapeutic apparatus capable of removing blood in an intravascular lumen to be observed using a minimally invasive method is provided. The apparatus includes high-intensity pulsed light generating means and high-intensity pulsed light transmitting means for transmitting high-intensity pulsed light, capable of irradiating the interior of a blood vessel with high-intensity pulsed light, producing water-vapor bubbles and temporarily removing the blood in the blood vessel.
