Cold HI gas appears as self-absorption dips in the 21-cm line profiles in and around the giant molecular cloud near W3 and W4. The cold HI cloud is ∼150 pc long and extends along the galactic plane. It consists of several fragments, each of which is typically ∼25 pc in diameter and (1 − 4) × 104 M⊙ in mass. The [H2]/[HI] ratio is estimated to be 15 – 50. The mass of the entire HI cloud amounts to ∼105 M⊙, which is comparable to that observed in CO emission.