To provide a base opening part reinforcing bar unit, minimizing connection and fixing work using welding or the like, reducing the number of parts, and requiring little trouble and time for managing and carrying the parts.

This base opening part reinforcing bar unit 1 includes: a pair of inverted L-shaped opening side end members 2 having an upper horizontal reinforcing bar 21 and a vertical reinforcing bar 22; an upper main reinforcement 3 and a lower main reinforcement 4 to which the vertical reinforcing bars of the paired opening side end members 2 are connected and fixed at designated distance so that the upper horizontal reinforcing bars are opposite to each other; two diagonal reinforcing bars 5 disposed on the opposite sides of the reinforcement 3 and the reinforcement 4; a lower horizontal reinforcing bar 6 connecting and fixing the lower end sides of the two diagonal reinforcing bars 5; a shearing reinforcing bar 7, the upper end part of which is fixed to the reinforcement 3 and the reinforcement 4, and the lower end part of which is provided with a hook piece 71 and fixed to the lower horizontal reinforcing bar 6 and the diagonal reinforcing bar 5; and a spacer 8 provided near the corner parts 23 of the upper horizontal reinforcing bar 21 and the vertical reinforcing bar 22 of the opening side end member 2 and connected and fixed to the main reinforcement 3 and the lowe main reinforcement 4.