In a fluidic device, a space (35) is formed in a passage block (26) to which a plurality of fluidic modules are connected and which is provided, in its inside, with fluid passages (43, 47, 51) for connecting the plurality of fluidic modules to one another. An internal body (36) is received in the space (35). Channels (37, 38, 39) are formed in an outer surface of the internal body so that the channels (37, 38, 39) constitute part of the fluid passages.