High-mass stars are highly influential in galaxy evolution by injecting a large amount of energy from ultraviolet photons, stellar winds, and supernova explosions. A theoretical scheme to explain the high-mass star formation is the monolithic collapse which assumes a compact dense core of 100 <i>M</i><sub>?</sub> within a volume of 0.1 pc radius (e.g., Krumholz et al. 2009). This condition is observationally constrained by the high-mass protostar objects including IRAS 05358+3543 in the Sh2-233 region (Beuther et al. 2007). However, the physical process to achieve such an unusually dense condition remains to be explored. In order to elucidate the process of forming the dense core, we have carried out a new kinematical analysis of the molecular gas in the Sh2-233 region by using the large-scale CO <i><b>J</b></i> = 2?1 data at a spatial resolution of ?0.5 pc. We find that the molecular clouds consist of two velocity components having a velocity difference of 2.7 km s<sup>-1</sup>. The red-shifted cloud is distributed in the southwest of the high-mass protostar, while the blue-shifted cloud in the northeast of the protostar. The two components are overlapped along a filamentary structure with a length of 5-pc and a width of 1.5-pc extending from the southeast to the northwest. The two dense core IRAS 05358+3543 and G173.58+2.45 are embedded in the filamentary structure. Based on these results, we frame a scenario where the two clouds collide and compress the gas between them to form the filament and two cores in ?0.5 Myr. We conclude that the super-sonic compression by a cloud-cloud collision collected a large amount of gas into a small volume and formed the massive dense cores as an essential initial process of high-mass star formation.