An optical mouse operated with respect to an illuminated surface outside the optical mouse is provided. The optical mouse includes a light source configured to emit a light beam, a light sensor, and a light pipe including a first optical element and a second optical element. The light beam enters the light pipe through the first optical element, and then propagates in the light pipe from the first optical element to the second optical element without reflection, and then leaves the light pipe through the second optical element, and then illuminates the illuminated surface. The light sensor is configured to receive at least a part of the light beam reflected or scattered by the illuminated surface.