A shield casing, which is configured to surround an electronic component mounted on a circuit board, includes a frame body including an engagement recess and a lid body including a hook unit configured to engage with the engagement recess. The lid body is fitted to the frame body to cover the frame body. The hook unit is elastically deformable in a second direction that is opposite to a first direction in which the lid body is fitted to the frame body as the lid body is fitted to the frame body, and then snaps into mating engagement in the engagement recess.