A fan speed controller of an automotive vehicle air conditioning device is usually placed in an air flow duct to be effectively cooled. Thus, compact construction of the speed controller is needed to obtain a larger air flow in the air flow duct. For this purpose, various compact resistor units for the speed controller have been proposed. However, some of them are poor in durability against shocks. In view of this, a compact resistor unit for a speed controller includes a resistor block that has a flat resistor, a flat insulating plate and a flat radiation plate which are respectively positioned against one another. The compact resistor unit further includes a holder block of molded plastic on which the resistor block is mounted. The compact resistor unit also includes a plurality of metal terminals partially embedded in the holder block, where the terminals are connected to particular portions of the flat resistor. The compact resistor still further includes metal connecting lugs that are partially embedded in the holder block, and rivets for securing the resistor block to the connecting lugs.