The present invention provides an asynchronous transmission device and asynchronous transmission method which reduce the synchronization processing overhead. The asynchronous transmission device that receives at least one notification signal in accordance with a reception clock, the notification signal being transmitted in accordance with a transmission clock, includes a trigger signal transmission unit that outputs a trigger signal which is based on the symbol period of the notification signal, a notification signal transmission unit that outputs a notification signal which has its timing staggered by a predetermined time period with respect to the timing of the trigger signal output from the trigger signal transmission unit, a trigger signal synchronization unit that synchronizes the trigger signal, and outputs a sampling timing signal which indicates the sampling timing of the notification signal, and a notification signal retention unit that retains the notification signal in accordance with the sampling timing.