A connector assembly comprising a connector (100, 100A) and a mating connector, wherein: the mating connector is mateable with and removable from the connector (100, 100A) along an up-down direction; the mating connector comprises a force-receiving portion; the connector (100, 100A) comprises a housing, a lever and a slider (400, 400A); the lever is attached to the housing so as to be rotatable between a first position and a second position; the slider (400, 400A) is attached to the housing so as to be movable in a front-rear direction perpendicular to the up-down direction; the lever has a pinion portion having pinion teeth; the slider (400, 400A) has a rack portion, a force-transmitting portion; the rack portion has rack teeth; the pinion portion and the rack portion are meshed with each other to convert a rotational movement of the lever into a movement of the slider (400, 400A) in the front-rear direction; the force-transmitting portion being configured as a cam groove transmits a force in the up-down direction to the force-receiving portion of the mating connector by the movement of the slider (400, 400A) in the front-rear direction; when the lever is rotated from the first position to the second position, the slider (400, 400A) is moved forward in the front-rear direction while the force-transmitting portion moves the force-receiving portion of the mating connector upward in the up-down direction so that the connector (100, 100A) and the mating connector are mated with each other; when the lever is rotated from the second position to the first position, the slider (400, 400A) is moved rearward in the front-rear direction while the force-transmitting portion moves the force-receiving portion of the mating connector downward in the up-down direction so that the connector (100, 100A) and the mating connector are in a state where the connector (100, 100A) and the mating connector are removable from each other; wherein the mating connector comprises a first pushing portion; the housing is provided with a housing regulating portion (220, 220A); the slider (400, 400A) has a regulated portion (450, 450A); characterized in that the housing regulating portion (220, 220A) and the regulated portion (450, 450A) are configured to engage with each other, when the lever is positioned at the first position under a state where the connector (100, 100A) and the mating connector are not mated with each other, so that the housing regulating portion (220, 220A) regulates a forward movement of the slider (400, 400A) and the first pushing portion is configured to push the housing regulating portion (220, 220A) or the regulated portion (450, 450A) to release regulation by the housing regulating portion (220, 220A), when the mating connector and the connector (100, 100A) are mated with each other. the mating connector is mateable with and removable from the connector (100, 100A) along an up-down direction; the mating connector comprises a force-receiving portion; the connector (100, 100A) comprises a housing, a lever and a slider (400, 400A); the lever is attached to the housing so as to be rotatable between a first position and a second position; the slider (400, 400A) is attached to the housing so as to be movable in a front-rear direction perpendicular to the up-down direction; the lever has a pinion portion having pinion teeth; the slider (400, 400A) has a rack portion, a force-transmitting portion; the rack portion has rack teeth; the pinion portion and the rack portion are meshed with each other to convert a rotational movement of the lever into a movement of the slider (400, 400A) in the front-rear direction; the force-transmitting portion being configured as a cam groove transmits a force in the up-down direction to the force-receiving portion of the mating connector by the movement of the slider (400, 400A) in the front-rear direction; when the lever is rotated from the first position to the second position, the slider (400, 400A) is moved forward in the front-rear direction while the force-transmitting portion moves the force-receiving portion of the mating connector upward in the up-down direction so that the connector (100, 100A) and the mating connector are mated with each other; when the lever is rotated from the second position to the first position, the slider (400, 400A) is moved rearward in the front-rear direction while the force-transmitting portion moves the force-receiving portion of the mating connector downward in the up-down direction so that the connector (100, 100A) and the mating connector are in a state where the connector (100, 100A) and the mating connector are removable from each other; wherein the mating connector comprises a first pushing portion; the housing is provided with a housing regulating portion (220, 220A); the slider (400, 400A) has a regulated portion (450, 450A); characterized in that the housing regulating portion (220, 220A) and the regulated portion (450, 450A) are configured to engage with each other, when the lever is positioned at the first position under a state where the connector (100, 100A) and the mating connector are not mated with each other, so that the housing regulating portion (220, 220A) regulates a forward movement of the slider (400, 400A) and the first pushing portion is configured to push the housing regulating portion (220, 220A) or the regulated portion (450, 450A) to release regulation by the housing regulating portion (220, 220A), when the mating connector and the connector (100, 100A) are mated with each other.