Aerospike nozzles have expected to be used for reusable space shuttles (single-stage-to-orbit: SSTO) to respond to growing demand for rocket launching at low cost. Unlike bell-type nozzles causing a big thrust loss due to over-expansion at low altitudes, aerospike nozzles expand combustion gas equilibrating with ambient pressure at any altitude, and the nominal expansion ratio is adjusted automatically to the suitable one. In this study, flow field structures in any cross sections around a linear-type aerospike nozzle are visualized and analyzed using NO-LIF. Since the flow field structures are affected mainly by the pressure ratio, the linear-type aerospike nozzle is set inside a vacuum chamber to carry out the experiments in the wide range of pressure ratios. A novel technique for measurement of surface pressure, the pressure sensitive paint (PSP) technique, is also applied successfully to measurement of the complicated pressure distribution on the spike surface. We have analysed flow fields of linear-type aerospike nozzles in detail by the two techniques for visualization and measurement, especially to demonstrate the effect of sidewalls to prevent the undesirable lateral expansion.