Particle species dependence of transverse momentum distribution as well as elliptic event anisotropy v2 have been beautifully described by hydrodynamic model calculation in terms of radial and elliptic collective expansion in high energy heavy ion collisions. Initial participant position fluctuation is also suggested as a source of triangular initial geometry, which could then expand collectively to form the final triangular event anisotropy v3 in momentum space. The first v3 measurements of identified particles at 200GeV Au+Au collisions from RHIC- PHENIX experiment will be presented. The collective triangular expansion behavior seen in v3 will be compared with hydro-dynamic model expectation in order to understand possible differences or similarities from the radial and elliptic expansion.