This paper summarizes final results of the K2K experiment which probes neutrino oscillation on accelerator produced neutrino beam sent over 250 km baseline toward the Super-Kamiokande detector. K2K collected 9.2 \times 10¹⁹ protons on target during its operation from 1999 to 2004. A total number of 112 beam induced neutrino events have been detected while 155.9^+11.5_-10.2 events were expected for no oscillation scenario. Incorporating into analysis a distortion of neutrino energy spectra an allowed region of 1.9 \times 10^-3 < \Delta m² < 3.5 \times 10^-3 {eV}² was obtained for sin²2 \theta = 1.0 in agreement with atmospheric neutrino results. A limit for transformation of muon neutrino into electron neutrino has been achieved at sin²2 \theta ₁₃ < 0.26 from one detected shower like data event.

PACS numbers: 14.60.Pq, 12.15.Ff