K2K long-baseline experiment is the first attempt to test atmospheric neutrino oscillation results under controlled beam conditions. It was found that the whole collected data sample disfavor no oscillation hypothesis at 4\sigma level. The full oscillation analysis of \nu _\mu \to \nu _x and \nu _\mu \to \nu _e transformations was performed using data set collected from June 1999 to July 2001. As a result we derive allowed region at 90\% CL of \Delta m² = 1.5 - 3.9 \times 10^-3 eV² for sin ² 2\theta _{\mu \tau} =1 consistent with atmospheric neutrino results. For \nu _e appearance search, an one observed event remains consistent with 2.4 \pm 0.6 background expectation. This allowed to obtain upper limit at 90\% CL of sin² 2\theta _{\mu e} < 0.15 for the best-fit \Delta m² from \nu _\mu disappearance analysis of 2.8 \times 10^-3 {eV}².

PACS numbers: 14.60.Pq, 14.60.Lm, 95.30.Cq, 95.55.Vj