This magnetic recording medium is characterized in that in the magnetic recording medium having a magnetic layer on a non-magnetic substrate by intercalating at least an under layer, the proportion of functional groups per 100 carbon atoms in a diamond-like carbon protective layer mainly composed of carbon for protecting the magnetic layer exceeds 20%. Certain embodiments may include an infrared laser pointer, a position sensitive detector, a visible laser pointer, and a control system. A funnel is formed at the upstream end of each of the intake branch pipes disposed within the intake air distribution box.