A bank angle detecting device includes a roll rate sensor for detecting a angular velocity ωr about a longitudinal axis of the motorcycle; a yaw rate sensor for detecting a angular velocity ωy about an vertical axis of the motorcycle; a bank angle detecting unit for detecting the motorcycle bank angle δ for calibration use based on the yaw rate ωy and a traveling velocity v; and a bank angle correcting unit for correcting the basic motorcycle bank angle δr, determined from an output ωr of the yaw rate sensor, so as to approach the motorcycle bank angle δ that is detected by the bank angle detecting unit, to thereby determine the estimated bank angle δ0.