To improve a capacity coefficient in a fluid coupling arranged between an engine and a transmission.

This fluid coupling 1 has a front cover 2, an impeller 3 and a turbine 4. A flow passage P formed in the axial direction between a first flow passage forming part 31b of an impeller 31 and a second flow passage forming part 41b of a turbine shell 41, includes a part enlarging in an axial directional dimension toward the inside in the radial direction or a part unchanging in the axial directional dimension.