Structural isomers of chloro[tri-tert-butyl-subphthalocyaninato]boron(III) (TBSubPc) molecules on the Au-(111) surface were identified by using the scanning tunneling microscope (STM). A TBSubPc is a corn-shaped and triangular molecule with a chloride atom at the top and three tert-butyl groups on its periphery. The molecule has four kinds of structural isomers depending on the binding sites of the tert-butyl groups. It can have two different adsorbed configurations on the surface, Cl-up and Cl-down. The STM image shows three spots that correspond to the three tert-butyl groups and one central spot that reflects the Cl atom. Analyzing the relative distances between the spots enables us to identify the isomers and the adsorbed configurations.