Patent ID: 8532893

Claim:
An automatic transmission comprising: a speed changer having a plurality of engagement elements and configured to shift the speed changer into a selected one of a plurality of shift stages by switching engaged and disengaged states of the engagement elements; a first rotation sensor for detecting input rotation of the speed changer and for outputting a pulse signal indicating the input rotation; a second rotation sensor for detecting output rotation of the speed changer and for outputting a pulse signal indicating the output rotation; and a controller comprising: an input-torque-change decision section for determining whether a change in input torque inputted into the speed changer occurs; and an interlock decision section for executing an interlock decision on whether interlock occurs in the speed changer, wherein the interlock decision section is configured to determine that interlock has occurred in the speed changer, when there is no pulse signal output from the second rotation sensor though, during a vehicle stopped state, the input-torque change has occurred and the pulse signal from the first rotation sensor has been outputted.