To provide a small-sized gas supply unit dispensing with connection parts or the like such as joints, pipes or the like among components or a gas supply unit facilitating maintenance of a manual valve or the like, the gas supply unit is provided with opening and closing valves for regulating flow of supply gas flowing in channels, a mass flow controller controlling the flow rate of the supply gas and a purge valve for supplying a replacement gas excluding the supply gas remaining in the mass flow controller, wherein a series of fixing blocks in which channels for making the supply gas and the purge gas flow are formed and which have first attaching portions for fixedly installing the opening and closing valves, the mass flow controller and the purge valve above the channels, are provided with second attaching portions by which fluid element parts communicating with the supply gas channels or the purge gas channels can be attached from a direction the same as that of the first attaching portion.