A wire-to-board connector comprising: a plug connector including a plug contact to which a wire is attached, and a plug housing that holds the plug contact; and a receptacle connector that is mounted on a connector mounting surface of a board and includes a receptacle contact corresponding to the plug contact, and a receptacle housing that holds the receptacle contact, the plug connector being mated with the receptacle connector to thereby allow the plug contact to contact the receptacle contact, wherein in a mated state in which the plug connector is mated with the receptacle connector, a vicinity portion of the wire, the vicinity portion being located in the vicinity of the plug connector extends along the connector mounting surface the board, a mating direction in which the plug connector is mated with the receptacle connector is a direction approaching the connector mounting surface of the board, the plug housing includes a plug side surface as a side surface of the plug housing the receptacle connector includes a side surface opposing portion that is opposed to the plug side surface in the mated state, the plug side surface is provided with a claw portion projecting toward the side surface opposing portion, the claw portion includes a plug lock surface that faces in a direction away from the connector mounting surface of the board and extends in a wire direction specified as a longitudinal direction of the vicinity portion in the mated state, the side surface opposing portion of the receptacle connector includes a receptacle lock surface that faces in a direction approaching the connector mounting surface of the board and is opposed to the plug lock surface in the mated state, the plug lock surface includes a lock maintaining surface disposed on a side in a connector wire direction in which the wire is viewed from the plug connector in the wire direction, and an unlocking surface disposed on a side in a wire connector direction which is opposite to the connector wire direction, and in a cross-section orthogonal to the wire direction, assuming that an angle formed between the lock maintaining surface and a reference plane that is a portion of the plug side surface located on a side farther from the connector mounting surface of the board than the claw portion is a lock maintaining angle (θ1) and an angle formed between the reference plane and the unlocking surface is an unlocking angle (θ2) the lock maintaining angle (θ1) is smaller than the unlocking angle (θ2). a plug connector including a plug contact to which a wire is attached, and a plug housing that holds the plug contact; and a receptacle connector that is mounted on a connector mounting surface of a board and includes a receptacle contact corresponding to the plug contact, and a receptacle housing that holds the receptacle contact, the plug connector being mated with the receptacle connector to thereby allow the plug contact to contact the receptacle contact, wherein in a mated state in which the plug connector is mated with the receptacle connector, a vicinity portion of the wire, the vicinity portion being located in the vicinity of the plug connector extends along the connector mounting surface the board, a mating direction in which the plug connector is mated with the receptacle connector is a direction approaching the connector mounting surface of the board, the plug housing includes a plug side surface as a side surface of the plug housing the receptacle connector includes a side surface opposing portion that is opposed to the plug side surface in the mated state, the plug side surface is provided with a claw portion projecting toward the side surface opposing portion, the claw portion includes a plug lock surface that faces in a direction away from the connector mounting surface of the board and extends in a wire direction specified as a longitudinal direction of the vicinity portion in the mated state, the side surface opposing portion of the receptacle connector includes a receptacle lock surface that faces in a direction approaching the connector mounting surface of the board and is opposed to the plug lock surface in the mated state, the plug lock surface includes a lock maintaining surface disposed on a side in a connector wire direction in which the wire is viewed from the plug connector in the wire direction, and an unlocking surface disposed on a side in a wire connector direction which is opposite to the connector wire direction, and in a cross-section orthogonal to the wire direction, assuming that an angle formed between the lock maintaining surface and a reference plane that is a portion of the plug side surface located on a side farther from the connector mounting surface of the board than the claw portion is a lock maintaining angle (θ1) and an angle formed between the reference plane and the unlocking surface is an unlocking angle (θ2) the lock maintaining angle (θ1) is smaller than the unlocking angle (θ2).