An electrical connection box includes a casing having an upper casing (10) and a lower casing (11). Terminal holes (19, 20) are formed on the outer wall of the casing. An insulating plate (12), mounted in the casing, has a several of wiring grooves (13) formed on at least one of its opposite faces (12a, 12b). Terminal driving portions (24 and 25), obtained by increasing a width of the wiring grooves (13), are provided at predetermined locations in the wiring grooves (13). Wires (14, 15) having first and second diameters are inserted into and held in the wiring grooves (13). Pressing contact terminals (16, 17) includes a pressing contact portion (16a, 17a) and an input-output terminal portion (16b, 17b) formed at its opposite ends, respectively. The pressing contact portions (16a, 17a) are driven into the terminal driving portions (24, 25) to connect through pressing contact to the wires (14, 15) held in the wiring grooves. The input-output terminal portions (16b, 17b) project out of each of the terminal holes (19, 20) to connect to an external circuit. The pressing contact portions (FIG. 46) may include notches (117g, 117h) that bite into the wiring groove as the pressing portions engage the wires and expand outwardly. Small-diameter wires 14 may engage shorter pressing contact terminals 16, while large-diameter wires 15 engage longer pressing contact terminals 17.