An electrical connection box (10), including: a relay (20) which has a locking projection (20K); and a connection box main body (30) which has a pressing projection (30K) that is engaged with the locking projection (20K), and which is formed with a storage space (30P) that stores the relay (20), in which a guide wall (30W) which is provided to stand on a boundary of the storage space is formed across the entire circumference of the boundary of the storage space in the connection box main body, and in which the pressing projection (30K) is formed at a narrow linking part (30B) of the guide wall in a direction in which the guide wall is provided to stand.