We report directional single mode emission in an InGaAsP semiconductor microcavity laser, which is composed of a circle and an isosceles trapezoid. When exciting a whole cavity, the laser generates a single mode without hopping in two directions over a wide range of continuous injection currents. In the emission spectrum, it is confirmed from the equidistant mode spacing that a scar mode becomes a single lasing mode above the lasing threshold. A numerical analysis of the boundary element method shows that the far-field pattern of the resonance agrees well with that of the experiment.