An auxiliary fitting jig includes first and second jig bodies configured to hold a connector from both sides of the connector, a first interval adjustment mechanism configured to interval-adjustably connect the first and second jig bodies, first and second lever bodies pivotally supported by the first and second jig bodies respectively, a second interval adjustment mechanism configured to interval-adjustably connect the first and second lever bodies in accordance with an interval between the first and second jig bodies adjusted by the first interval adjustment mechanism.