UNIT

To provide a unit having improved heat exchange efficiency. A unit (1) includes a housing (HS) configured to accommodate a planetary gear mechanism (4), wherein the housing (HS) includes a flow path (CP1) through which a coolant flows, the planetary gear mechanism (4) includes a stepped pinion gear (43), the stepped pinion gear (43) includes a small pinion (432) and a large pinion (431), and the flow path (CP1) has a portion that overlaps the large pinion (431) when viewed in a radial direction.