The waterproof casing has a housing and a grommet. The grommet is disposed in a hole of the housing. The grommet has a body, a flange, and a lip. The flange extends radially outward from the body. The lip protrudes from an outer peripheral part of the body and extends in a circumferential direction. The lip has a high compression portion in contact with a wall surface of the hole and a low compression portion adjacent to the high compression portion at a further side from the flange. The low compression portion has a lower compressed state than the high compression portion. The housing has a recess to allow the low compression portion to escape radially outward.