A circuit-terminal connecting device comprising; a first connector having a first insulating housing and a plurality of first contacts, each of said first contacts being supported by the first insulating housing to have a board-connecting port i on operative to be connected with a cor respond i ng one of first circuit-terminals provided on a main circuit board to which the first insulating housing can be fixed, and a second connector (14; 40) having a second insulating housing (17; 41) provided with an engaging portion (21; 43) for engaging with the first connector and a plurality of second contacts (18; 42), each of said second contacts (18; 42) being supported by the second insulating housing (17; 41) to have a terminal-connecting portion (26; 47) operative to be connected with a corresponding one of second circuit-terminals provided on a flat circuit member to which the second insulating housing (17; 41) can be attached, wherein the second insulating housing (17; 41) of the second connector (14; 40) can be fixed to a hole-forming portion of the flat circuit member with the engaging portion (21; 43) thereof fitting into an engaging hole formed in the hole-forming portion, wherein the engaging portion (21; 43) of the second insulating housing (17; 41) of the second connector (14; 40) forms a hole (22; 44) therein into which the first insulating housing of the first connector fits, wherein each of the first contacts of the first connector is provided with a contact-engaging portion extending from an outer surface of the first insulating housing of the first connector to the outside of the same, wherein each of the second contacts (18; 42) of the second connector (14; 40) is provided with a contact-connecting portion (25; 46) positioned to face to the hole (22; 44) formed in the second insulating housing (17; 41) of the second connector (14; 40), and, wherein the contact-connecting portion (25; 46) of the second contact (18; 42) of the second connector (14; 40) comes into contact with the contact-engaging portion of the first contact of the first connector to be connected with the same, so that the first circuit-terminals provided on the main circuit board can be connected respectively with the second circuit-terminals provided on the flat circuit member through the first and second contacts (12, 14; 40) when the first insulating housing of the first connector fits into the hole (22; 44) formed in the second insulating housing (17; 41) of the second connector (14; 40), characterized in that the first connector is provided with a locking projection (33A; 33B) operative to project from a portion of the first connector positioned in the hole (22; 44) formed in the second insulating housing (17; 41) of the second connector (14; 40) so as to engage with a receiving portion (35A; 35B, 48A; 48B) formed on a part of the engaging portion (21; 43) of the second insulating housing (17; 41) of the second connector (14; 40) and thereby to lock the second connector (14; 40) when the first insulating housing of the first connector fits into the hole (22; 44) formed in the second insulating housing (17; 41) of the second connector (14; 40), and wherein the first connector is further provided with a metallic holding member (30A; 30B) for engaging with the first insulating housing from the outside of the same to be used for attaching the first insulating housing of the first connector to the main circuit board and the locking projection (33A; 33B) is provided in the metallic holding member (30A; 30B) as a resilient portion projecting from the metallic holding member (30A; 30B) to the outside of the same.