To improve accuracy in slip angle estimation and to improve accuracy particularly in the initial period of steering and at the time of switching steering.

This detecting device is provided with a slip angle estimating means (e) for estimating a slip angle of a vehicle on the basis of input from a steering angle sensor (a), a vehicle speed sensor (b), a lateral acceleration sensor (c) and a yaw rate sensor (d). The slip angle estimating means (e) is provided with a first slip angle estimating part e3 estimating the slip angle on the basis of the tire stiffness estimate which is side force per unit slip angle of a wheel; a second slip angle estimating part e4 estimating the slip angle on the basis of the integrated value of lateral acceleration, yaw speed and travel speed; an immediately-after-steering judging part e5 for judging whether to be immediately after steering; and an estimation switching part e6 for making the second slip angle estimating part e4 estimate the slip angle in the case of judging immediately after steering and making the first slip angle estimating part e3 estimate the slip angle with the exception of the case of judging immediately after steering.