A test pattern generator for automatically generating a test pattern for detecting a stack fault of a large scale integrated circuit an LSI with a tester includes a loop/path disconnecting section for disconnecting a loop portion of the LSI at a position where a fault detection rate is not lowered, based on net list information of the LSI and constraint of a test design rule when automatically generating the test pattern. A test pattern generator increasing fault detection rate and carrying out a suitable test is obtained.