We have observed a “K− pp”-like structure in the d(π+, K+) reaction at 1.69 GeV/c. In this reaction, a (1405) hyperon resonance is expected to be produced as a doorway to form K− pp through the 
∗ p → K− pp process. However, most of the (1405) produced would escape from the deuteron without secondary reactions. Therefore, coincidence of high-momentum (>250MeV/c) proton(s) at large emission angles (39◦< θlab. < 122◦) was requested to enhance
the signal-to-background ratio. A broad enhancement in the proton coincidence spectra is observed around the missing mass of 2.27 GeV/c2, which corresponds to the K− pp binding energy of 95 +18
−17 (stat.) +30 −21 (syst.) MeV and the width of 162 +87 −45 (stat.) +66 −78 (syst.) MeV.