Provided is a connector box having high durability. The connector box includes a receptacle connector portion having a connector insertion opening into which a plug connector is inserted from the front side, a circuit board unit having the receptacle connector portion at a front end of a circuit board, a casing configured to accommodate the circuit board unit with the connector insertion opening being opened to the outside. The casing includes a lower casing for covering a lower face of the circuit board unit and an upper casing for covering an upper face of the circuit board unit and engagedwith the lower casing. In association with sliding of the upper casing to one side in the front/rear direction, the upper casing is engaged with the lower casing.