The growth of long-haul truck transportation the increase in the number of aged drivers, as well as an increasing demand for a driving work environment have caused the current need for easier and more automated driving operations for heavy vehicles. Also, work is under way to make various improvements and developments in ease of operation of heavy vehicles.One such field where active work is taking place is the automation of transmission. In the passenger car field, over 50 % of cars currently placed on the domestic market have a torque converter type automatic transmission. As for heavy vehicles, however, automatic transmission is not popular in our market despite the merits it offers for ease of operation. This is because of its high cost and higher fuel consumption (10 % to 20 % more than comparative vehicles with manual transmission).On the other hand, with recent progress in electronic control technology, we have come to develop automatic transmission systems that are capable of achieving control of the power plant equivalent to human control by means of electronic control of the power plant of manually operated vehicles. One of the merits of such a system is that parts that have proven themselves well in manually operated vehicles can be used as they are in the main portions of the power line. Furthermore, with such a system, fuel consumption equivalent or superior to conventional manually operated vehicles can be anticipated, and conventional manufacturing facilities can be used as they are. In view of these points, it is expected that such systems will become one of the most important automatic transmission systems for heavy trucks and buses.At Mitsubishi Motors Corp., we have also developed a mechanical clutch automatic transmission system that makes use of a clutch and sychromesh gear transmission that are similar to those used in manually operated vehicles. The system named the Mitsubishi Mechanical Automatic Transmission System (MMAT system), is introduced in the following section.