The J-PARC E36 experiment is aiming at searching for the lepton universality violation by precisely measuring the ratio of the branching
ratio of the $K^+ \rightarrow e^+ \nu$ ($K_{e2}$) and $K^+ \rightarrow \mu^+\nu$ ($K_{\mu 2}$) decays.he E36 experiment was performed at J-PARC employing a stopped $K^+$ beam in conjunction with a 12-sector iron-core superconducting toroidal spectrometer. Charged particle momentum was calculated by reconstructing the tracks in the spectrometer. Particle discrimination between $e^+$ and $\mu^+$ was carried out using an aerogel Cherenkov counters and a lead-glass Cherenkov counter, as well as by measuring the time-of-flight between TOF counters. The peak structure due to the $K_{e2}$ decays was successfully observed in the $e^+$ momentum spectrum. The structure-dependent radiative $K^+ \rightarrow e^+ \nu
\gamma$ ($K_{e2 \gamma}$) events can be selected by requiring one photon hit in the CsI(Tl) calorimeter. The experimental spectra were reproduced by the Monte Carlo simulation, which indicates a correctunderstanding of the experimental conditions.