To constrain swelling of parallel opposed surfaces of a skeleton by engagingly locking a reinforcing bar arranged on the outer surface of the skeleton to a constraining bar inserted to a through-hole, engagingly fixing a hook on the reinforcing bar, and connecting a plurality of the hooks to both ends of a through-bolt substituted for a constraining bar.

In a construction method of reinforcing a concrete structure 1 having an oval sectional skeleton by constructing a concrete for reinforcing 3 on an existing skeleton concrete 2 to extend the section, a through-hole 5 is bored between opposed parallel surfaces, a through-bolt 12 is inserted thereto, and reinforcing bar engaging fixing jigs 11 are screwed and constrained to both the ends thereof on the existing wall body outer surface. The reinforcing bar fixing jig 11 has two fixing arms having hooks on the tips, and a reinforcing bar 4 is engagingly fixed to the hooks. Thus, the number of through-holes to be bored in the concrete structure can be minimized, a constraining bar is dispensed with, and the hook having the reinforcing bar fixed thereto by a bolt can be firmly fixed to the skeleton outer surface.