A series of police doppler single mode radars and a multimode police doppler radar, all with direction sensing capability are disclosed. Each register includes an input port selector for selecting one of the write ports through which data is received. When a size of the stored data is inquired from the source apparatus, the sink apparatus informs the size to the source apparatus. Control logic simply increases an increment of reaction force between a first reaction force increment and a second reaction force increment as the determined degree of risk grows from a predetermined cutoff value to a predetermined critical value to determine the command for regulating the actuator to realize the increment in reaction force.