This is an interesting one. Sugiyama shows only an earlier model (no bayonet mounts, a slower shutter and a very different nameplate); it is listed as "maker unknown", with four-star rarity. McKeown has two models: the first the same as the Sugiyama one; the second the same as mine shown here - both listed without maker attribution.
This one turned up in someone's cupboard in a camera bag also containing a Yashica-44 and various filters and supplementary (telephoto) lenses. Fortunately, the seller listed all this in an obscure corner of eBay, and I was able to buy the lot quite cheaply!
It's a conventional design, which McKeown dates - correctly I think - as c1955. What put me on a trail was the letters "LKK" on the flash shoe. Looking through the catalogues, the most likely candidate for these initials is "Lustre Optical Works" (maker of the Lustreflex below) My Japanese is very limited indeed, but the word "koki" means something like "optics" and routinely appears in lensmakers' and camera manufacturers' names. Various other words such as "kogaku" (="ancient learning") or "koken" are often strung alongside it. I therefore think "Luster Koki K~" is a distinct possibility.
Comparing the Echoflex to my Lustreflex and to another shown in Sugiyama clinched this for me. The bodies are identical, as are most of the fitments (to one or other Lustreflex model) - catch, knobs, strap mount, counter, etc.
The only residual mystery is, why was it made - did Lustre make it for a distributor? The manual cover (below) says the "sole distributor was "Transvision Trading Co. of Tokyo" - now apparently out of business for some time - with no manufacturer mentioned. The stamp above that is from Burlington Cameras in the Burlington Arcade in London (I think long-defunct), who sold it, and who must have been a fairly classy outfit at that address.
Taking lens is Echor Anastigmat 75mm f3.5
Shutter is Synchro-Super 1 to 1/300