A noble measurement method for planar elongation viscosity was proposed. A bullet shaped bob was pushed into a sample liquid held in a cylindrical cup with a constant velocity and the resistance force acting on the bullet bob was measured. The bullet bob was designed to generate steady planar elongation flow through the gap between the bob and the cup. The trial experiments were carried out for standard viscous fluids and aqueous polymer solutions. The resistant forces were measured as a function of the planar elongation rate. The forces were compared to flow analysis of Newtonian, non-Newtonian and viscoelastic fluids. These forces were generally consistent with experimental data.