A connector unit comprising: a first connector having a rod-shaped first terminal fitting, a tube-shaped first housing arranged to receive the first terminal fitting and a contact-preventive housing disposed between the first terminal fitting and the first housing, the contact-preventive housing including an aperture through which the first terminal fitting is passed and being arranged to slide along a longitudinal direction of the first terminal fitting; and a second connector having a second terminal fitting to be connected to the first terminal fitting and a second housing arranged to receive the second terminal fitting and arranged to fit with the first housing, wherein the contact-preventive housing includes a tension spring having one end fixed at an outer circumference of the contact-preventive housing and the other end arranged as a free end, the other end extending away from the second connector along the longitudinal direction, being adapted to be engaged to an engagement receiving portion of the first housing thereby restricting the contact-preventive housing from sliding, the tension spring including a tapered portion slanted away from the contact-preventive housing in a direction from the one end to the other end of the tension spring, wherein the second housing includes an entering portion arranged to enter between the tension spring and the first housing when moved towards the first housing and pushes the tapered portion towards the contact-preventive housing, thereby making the other end of the tension spring disengaged from the first housing to permit the contact-preventive housing to slide, characterized in that the connector unit further comprising: a return spring attached to the outer circumference of the contact-preventive housing; and a slanted face provided at an inner circumference of the first housing, the slanted face being slanted towards the first terminal fitting in a direction away from the second connector, wherein the return spring includes an abutting portion arranged to project towards the slanted face so as to abut on the slanted face. a first connector having a rod-shaped first terminal fitting, a tube-shaped first housing arranged to receive the first terminal fitting and a contact-preventive housing disposed between the first terminal fitting and the first housing, the contact-preventive housing including an aperture through which the first terminal fitting is passed and being arranged to slide along a longitudinal direction of the first terminal fitting; and a second connector having a second terminal fitting to be connected to the first terminal fitting and a second housing arranged to receive the second terminal fitting and arranged to fit with the first housing, wherein the contact-preventive housing includes a tension spring having one end fixed at an outer circumference of the contact-preventive housing and the other end arranged as a free end, the other end extending away from the second connector along the longitudinal direction, being adapted to be engaged to an engagement receiving portion of the first housing thereby restricting the contact-preventive housing from sliding, the tension spring including a tapered portion slanted away from the contact-preventive housing in a direction from the one end to the other end of the tension spring, wherein the second housing includes an entering portion arranged to enter between the tension spring and the first housing when moved towards the first housing and pushes the tapered portion towards the contact-preventive housing, thereby making the other end of the tension spring disengaged from the first housing to permit the contact-preventive housing to slide, characterized in that the connector unit further comprising: a return spring attached to the outer circumference of the contact-preventive housing; and a slanted face provided at an inner circumference of the first housing, the slanted face being slanted towards the first terminal fitting in a direction away from the second connector, wherein the return spring includes an abutting portion arranged to project towards the slanted face so as to abut on the slanted face. a return spring attached to the outer circumference of the contact-preventive housing; and a slanted face provided at an inner circumference of the first housing, the slanted face being slanted towards the first terminal fitting in a direction away from the second connector, wherein the return spring includes an abutting portion arranged to project towards the slanted face so as to abut on the slanted face.