An electrical connector including: a connector housing having a slot into which a circuit board formed in a mating connector is to be inserted; and a plurality of connector terminals to be inserted into the connector housing, the connector housing including terminal spaces into which the connector terminals are inserted, partition walls partitioning the terminal spaces from adjacent ones, the connector terminals each including a sheath to be inserted into one of the terminal spaces, and a resilient contact making electrical contact with the circuit board, wherein the electrical connector includes means for preventing the terminal spaces and the circuit board from falling apart from each other, the means comprising a convexity (118, 121c) formed at one of the at least one of opposite sidewalls of the sheath and the partition wall or partition walls, and a concavity (116, 121f) into which the convexity (118, 121c) is fit, the concavity (116, 121f) being formed at the other of the at least one of opposite sidewalls of the sheath and the partition wall or partition walls, characterized by a circular slot into which a mating connector housing of the mating connector is inserted, and in that the circular slot having a first portion including an opening having a thickness greater than a thickness of the mating connector housing, and a second portion located at a back of the first portion and having a width smaller than the same of the first portion in order for the mating connector housing of the mating connector to be inserted thereinto, the means is formed on opposite sidewalls of the sheath and partition walls facing the opposite sidewalls of the sheath, and a convexity (118, 121c) formed at one of the opposite sidewalls of the sheath or the partition wall facing the one of the opposite side walls of the sheath is located at a different height from a convexity (118, 121c) formed at the other of the opposite sidewalls of the sheath or the partition wall facing the other of the opposite sidewalls of the sheath. a connector housing having a slot into which a circuit board formed in a mating connector is to be inserted; and a plurality of connector terminals to be inserted into the connector housing, the connector housing including terminal spaces into which the connector terminals are inserted, partition walls partitioning the terminal spaces from adjacent ones, the connector terminals each including a sheath to be inserted into one of the terminal spaces, and a resilient contact making electrical contact with the circuit board, wherein the electrical connector includes means for preventing the terminal spaces and the circuit board from falling apart from each other, the means comprising a convexity (118, 121c) formed at one of the at least one of opposite sidewalls of the sheath and the partition wall or partition walls, and a concavity (116, 121f) into which the convexity (118, 121c) is fit, the concavity (116, 121f) being formed at the other of the at least one of opposite sidewalls of the sheath and the partition wall or partition walls, characterized by a circular slot into which a mating connector housing of the mating connector is inserted, and in that the circular slot having a first portion including an opening having a thickness greater than a thickness of the mating connector housing, and a second portion located at a back of the first portion and having a width smaller than the same of the first portion in order for the mating connector housing of the mating connector to be inserted thereinto, the means is formed on opposite sidewalls of the sheath and partition walls facing the opposite sidewalls of the sheath, and a convexity (118, 121c) formed at one of the opposite sidewalls of the sheath or the partition wall facing the one of the opposite side walls of the sheath is located at a different height from a convexity (118, 121c) formed at the other of the opposite sidewalls of the sheath or the partition wall facing the other of the opposite sidewalls of the sheath.