Recently, Hamaguchi et. al (Proc.12^<th> ISEC, 2005, p.275) proposed a new engine called "Pulse Tube Engine", which uses extremely simple hardware consisting of a few parts. We built a prototype pulse tube engine using one atmospheric pressure air as the working gas and experimentally studied the working mechanism from the standpoint of thermoacoustic framework. The work flux distribution over the cross-section of the pulse tube was determined through simultaneous measurement of pressure and velocity in order to find out the work source of the engine. We will report in this workshop that the pulse tube engine is classed as the thermoacoustic standing-wave engine group relying on intrinsically irreversible thermodynamical process, which is different from Stirling engine relying on intrinsically reversible process.