Semiconductor integrated circuit device with diagnosis function

A logic LSI is divided into a plurality of functional blocks, and an output portion of each functional block is provided with a buffer circuit with a scan function which can change a function of latching data by a control signal and a function of making an input signal pass intact. The buffer circuit is connected to a test exclusive bus and the test data can be entered directly to the buffer or read out of the buffer. Test patterns are generated in each functional block and diagnosis can be carried out in each functional block. When the functional block is used in other LSI, since the test patterns already generated can be utilized, the time required for generation of test patterns and for the test can be significantly reduced.