at the lower end of terminal block 9 2 the adjusting segment 59 has an about l shaped opening 60 a push up engagement 61 and a push down engagement 62 and is provided at one end with a projection 14 onto which an engaging bore 15a at bimetal 15 is fixedly fitted the terminal block 9 2 is formed of a plate such as copper or copper alloy sheet for better electric conductivity so that the adjusting segment 59 is relatively easy to deform and when the push up jig 57 engages with the push up engagement 61 to push the adjusting segment 59 upwardly the opening 60 is deformed at its surrounding portions and the free end of bimetal 15 shifts in the direction of the arrow q when the push down jig 58 engages with the push down engagement 62 to push the adjusting segment 59 downwardly the surrounding portion of opening 60 is deformed reversely whereby the free end of bimetal 15 shifts in the reverse direction to the arrow q hence a gap between the free end of bimetal 15 and the abutting segment 42 at the latch plate 37 is desirably adjustable thereby enabling adjustment of the thermal response characteristic of bimetal 15 next a modified embodiment of the invention will be shown in fig1 through 13 in which three circuit breakers b as aforesaid are juxtaposed to constitute a three phase ac circuit breaker each circuit breaker b being fixed with each other by fixtures 3 as shown in fig1 each handle 4 is covered at its operating portion with a connecting cap 63.