Spatial restrictions were imposed on the inner layer structure of the turbulent boundary layer which was developing on a moving flat-plate, by means of putting a fixed array of vertical plates close to the moving plate. The nondimensional gap h+ between the flat-plate and the tips of the interfering vertical plates as well as the nondimensional pitch p+ of the interfering plates were systematically changed. From hot-film anemometer measurements, states of flows were distinguished into three regions in the h+ vs. p+ plane, i. e., laminar, transitional, and fully turbulent regions. With increase in the pitch p+, the gap h+ needed to maintain turbulence decreased mildly from 40. This was explained with a view of the distribution of sizes of the coherent structures in the inner layer.