Device having a power transmission mechanism

A unit comprising:

• a gear device including a first planetary gear mechanism including a first sun gear, a first carrier, and a first ring gear, and a second planetary gear mechanism including a second sun gear, a second carrier, and a second ring gear;
• an input element;
• an output element;
• a first engagement element;
• a second engagement element;
• and
• a third engagement element,
• wherein the first sun gear and the second carrier are coupled to each other to rotate integrally,
• the second sun gear and the first carrier are coupled to each other to rotate integrally,
• one side of the first engagement element is connected to the input element,
• the other side of the first engagement element is connected to the first sun gear and the second carrier,
• one side of the second engagement element is connected to the input element,
• the other side of the second engagement element is connected to the second ring gear,
• one side of the third engagement element is connected to the second sun gear and the first carrier,
• the other side of the third engagement element is fixed, and
• the output element is connected to the first ring gear.