A first electrical connection box includes a housing, a holder (40) that is provided inside the housing, and holds an electrical component (51) to which a first wire (21) is to be electrically connected; and a terminal block (60) attached to the holder (40). The terminal block (60) includes a terminal support base (61) attached to the holder (40), and a busbar (62) supported on the terminal support base (61). The busbar (62) includes a planar first connection surface (84), and a planar second connection surface (86) to which a second wire (22) is to be electrically connected. Also, the first electrical connection box further includes a relay busbar (90) that is provided inside the housing, and includes a third connection surface (97) that is electrically connected to the first connection surface (84), and a fourth connection surface (99) that is electrically connected to the electrical component (51).