Lens barrel and imaging device

A lens barrel comprising:

• an electromechanical conversion element;
• an elastic body which has a joining surface on which the electromechanical conversion element is joined and a drive surface on which a vibration wave is generated due to vibration of the electromechanical conversion element, the elastic body on which a plurality of grooves are formed;
• a motion member which makes contact with the drive surface and is configured to rotate by the vibration wave;
• a rotating ring which has a recess part and is configured to rotate by rotation of the motion member;
• a moving ring which has a protrusion part engaged to the recess part and is configured to move to an optical axis direction by rotation of the rotating ring;
• and
• a lens which is held in the moving ring;
• wherein the electromechanical conversion element is made of a material having sodium potassium niobate, potassium niobate, sodium niobate or barium titanate as a principle component,
• wherein a value of T/(B+C) is within a range of from 1.3 to 2.8 when:
• length from the drive surface to a base unit of at least one groove of the plurality of grooves is defined as T;
• length from the base unit of the groove to the joining surface is defined as B;
• and
• thickness of the electromechanical conversion element is defined as C.