Formation mechanism of a supergiant HII region NGC604 is discussed in terms of collision of HI clouds in M33. An analysis of the archival HI data obtained with the Very Large Array (VLA) reveals complex velocity distributions around NGC604. The HI clouds are composed of two velocity components separated by ∼20km s-1 for an extent of ∼700 pc, beyond the size of the the HII region. Although the HI clouds are not easily separated in velocity with some mixed component represented by merged line profiles, the atomic gas mass amounts to 6 × 106 M⊙ and 9 × 106 M⊙ for each component. These characteristics of HI gas and the distributions of dense molecular gas in the overlapping regions of the two velocity components suggest that the formation of giant molecular clouds and the following massive cluster formation have been induced by the collision of HI clouds with different velocities. Referring to the existence of a gas bridging feature connecting M33 with M31 reported by large-scale HI surveys, the disturbed atomic gas possibly represents the result of past tidal interaction between the two galaxies, which is analogous to the formation of the R136 cluster in the LMC.