A connector comprising: a connector position assurance device movable between a first position and a second position different from the first position, and upon being at the second position, assuring that the connector is completely-mated with a mating connector, or maintaining the completely-mated state; and a housing having a mating portion to join with the mating connector, and a guiding portion provided at a rear farther from the mating connector than the mating portion or provided from the rear to the mating portion to guide movement of the connector position assurance device between the first position and the second position, wherein the connector position assurance device has a base portion guided by the guiding portion, and a beam portion protruding from the base portion to the mating portion, the housing has an abutting portion abutting on the beam portion of the connector position assurance device in the first position during non-mating with the mating connector to block movement of the connector position assurance device to the second position, and the beam portion is configured to be deformed by the mating connector during complete mating to remove the abutment of the beam portion on the abutting portion to allow the connector position assurance device to move to the second position, the guiding portion has two guiding rails slidably holding the base portion of the connector position assurance device from both widthwise sides crossing the sliding direction, the base portion has two beams extending in the sliding direction along each of the two guiding rails, and a guided portion, a spaced portion spaced from the guiding rail, a bulging portion bulging toward the guiding rail within the spaced portion, and a retaining portion adjacent to a front of the spaced portion and protruding toward the guiding rail are provided on the external side face of each of the two beams, the guiding portion has a protruding portion protruding from the guiding rail in front of the bulging portion when the connector position assurance device is in the first position to interfere with the bulging portion when the connector position assurance device in the first position moves to the second position to give resistance to the movement, characterised in that the guided portion is a portion which is in contact with the guiding rail and with which sliding of the connector position assurance device is guided, and the spaced portion is a portion adjacent to a front of the guided portion. a connector position assurance device movable between a first position and a second position different from the first position, and upon being at the second position, assuring that the connector is completely-mated with a mating connector, or maintaining the completely-mated state; and a housing having a mating portion to join with the mating connector, and a guiding portion provided at a rear farther from the mating connector than the mating portion or provided from the rear to the mating portion to guide movement of the connector position assurance device between the first position and the second position, wherein the connector position assurance device has a base portion guided by the guiding portion, and a beam portion protruding from the base portion to the mating portion, the housing has an abutting portion abutting on the beam portion of the connector position assurance device in the first position during non-mating with the mating connector to block movement of the connector position assurance device to the second position, and the beam portion is configured to be deformed by the mating connector during complete mating to remove the abutment of the beam portion on the abutting portion to allow the connector position assurance device to move to the second position, the guiding portion has two guiding rails slidably holding the base portion of the connector position assurance device from both widthwise sides crossing the sliding direction, the base portion has two beams extending in the sliding direction along each of the two guiding rails, and a guided portion, a spaced portion spaced from the guiding rail, a bulging portion bulging toward the guiding rail within the spaced portion, and a retaining portion adjacent to a front of the spaced portion and protruding toward the guiding rail are provided on the external side face of each of the two beams, the guiding portion has a protruding portion protruding from the guiding rail in front of the bulging portion when the connector position assurance device is in the first position to interfere with the bulging portion when the connector position assurance device in the first position moves to the second position to give resistance to the movement, characterised in that the guided portion is a portion which is in contact with the guiding rail and with which sliding of the connector position assurance device is guided, and the spaced portion is a portion adjacent to a front of the guided portion.