An method of, and an apparatus for, converting layout data of a conductive portion is obtained in which conversion of layout data of the conductive portion is automatically performed in a reduced processing time, designing is performed efficiently, and development stages are reduced in number. The layout data conversion apparatus comprises a basic pattern unit (basic layout pattern), a storage means 1, a design rule memory means 2, a means for storing information about connection between basic pattern units 3, a basic layout pattern generation means 4, a connection determination means 5 for determining whether conductive portions are connected to each other a layer information determining means 6, an element configuration change means 7, a means for detecting and eliminating violation of design rules 8, a means for storing and displaying layout pattern arrangement result information 9, and a computation control means 10 for controlling operations of these means.