To reasonably arrange an embedded box so as to closely contact with a flask even when a reinforcing bar and the flask are at a short distance.

An embedded box device 1 is fitted with a support member 2 for fixing the embedded box 1 by being extended between two reinforcing bars 3 arranged in parallel, the support member 2 comprises first metal fittings 2a fixed to the embedded box 1 and having a first connection portion 10 coupled to one of the reinforcing bars 3, second metal fittings 2b coupled to the first metal fittings 2a to a proper length and having a second coupling portion 20 coupled to the other reinforcing bar 3, and the support member 2 is manufactured so that the front of the embedded box 1 abuts against a flask 4 of reinforced concrete while the embedded box 1 is fixed by coupling the support member 2 to the reinforcing bars 3.