The present invention provides a method and an apparatus for preparing a silicon-containing solid film, which can form a thin film uniformly over a wide area. Raw-material fluid comprising a silane derivative and a hydrocarbon derivative is mixed with carrier fluid comprising carbon dioxide to form a supercritical condition. Further, an active-state is produced in the raw-material fluid of the supercritical fluid by a catalytic reaction with at least one metal catalyst selected from a group consisting of platinum, tungsten, cobalt, nickel, iron or an alloy of each of them. The fluid is blown to the substrate, thereby forming a silicon-containing solid film or a hydrocarbon-containing solid film on the substrate.