From Oita Airport you can rent a car, take a taxi (taxi stands are in front of the passenger terminal), or a bus (Bus stops 1, 2 & 3 are across from International Arrivals) and the Hovercraft Boarding slip is across from the charter bus parking lot.The Horbar Hovercraft.

Specific color bus stops are marked for the following bus routes:
Green: for bus to Oita via Beppu - taking 60 minutes; (46 mins to Beppu Station)
Pink:  for bus to Beppu-Eki Mae - taking 46 minutes;
Purple:  for bus to Yufuin - taking 55 minutes;
Brown: for bus Nakatsu Usa, bound for Bungo-Takada - taking 110 minutes
Blue:  for bus to Salki - taking 127 minutes.

Google Plus One