Automatic transmission

An automatic transmission, comprising:

• an input member disposed inside a casing and rotated by a driving force transmitted from a drive source;
• a planetary gear mechanism, wherein each of which has a plurality of elements rotatable inside the casing;
• a plurality of engagement mechanisms switchable to a coupled state in which the elements are coupled to one another, or switchable to a fixed state in which the elements are fixed to the casing, comprising:
• a switching mechanism switchable between the fixed state and a reverse rotation preventing state that allows a normal rotation and prevents a reverse rotation of corresponding elements among the plurality of elements;
• an output member outputting a rotation;
• a control part controlling the engagement mechanisms and recognizes a rotational frequency of the drive source;
• and
• a switching control circuit switching the engagement mechanism according to a signal from the control part, comprising
• a switching part switching the switching mechanism to the reverse rotation preventing state or the fixed state and
• a switching part state detector transmitting a signal indicating a state of the switching part to the control part,
• wherein
• the automatic transmission is configured to output a rotation of the input member from the output member while changing speed in a plurality of gear positions with the planetary gear mechanism and the engagement mechanisms, and
• in the case where the drive source is determined to be in a stopped state by the control part, if the state of the switching part does not correspond to a state that the control part instructed before the drive source is determined to be in the stopped state, the control part transmits a signal for switching the switching mechanism to a state corresponding to the state of the switching part to the switching control circuit.