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The light curve of the microlensing event KMT-2021-BLG-1898 exhibits ashort-term central anomaly with double-bump features that cannot be explainedby the usual binary-lens or binary-source interpretations. With the aim ofinterpreting the anomaly, we analyze the lensing light curve under varioussophisticated models. We find that the anomaly is explained by a model, inwhich both the lens and source are binaries (2L2S model). For thisinterpretation, the lens is a planetary system with a planet/host mass ratio of$q\sim 1.5\times 10^{-3}$, and the source is a binary composed of a turn off ora subgiant star and a mid K dwarf. The double-bump feature of the anomaly canalso be depicted by a triple-lens model (3L1S model), in which the lens is aplanetary system containing two planets. Among the two interpretations, the2L2S model is favored over the 3L1S model not only because it yields a betterfit to the data, by $\Delta\chi^2=[14.3$--18.5], but also the Einstein radiiderived independently from the two stars of the binary source result inconsistent values. According to the 2L2S interpretation, KMT-2021-BLG-1898 isthe third planetary lensing event occurring on a binary stellar system,following MOA-2010-BLG-117 and KMT-2018-BLG-1743. Under the 2L2Sinterpretation, we identify two solutions resulting from the close-widedegeneracy in determining the planet-host separation. From a Bayesian analysis,we estimate that the planet has a mass of $\sim 0.7$--0.8~$M_{\rm J}$, and itorbits an early M dwarf host with a mass of $\sim 0.5~M_\odot$. The projectedplanet-host separation is $\sim 1.9$~AU and $\sim 3.0$~AU according to theclose and wide solutions, respectively.

KMT-2021-BLG-1898: Planetary microlensing event involved with binary source stars