The present invention provides a cesium-lithium-borate crystal, which can be used as a high-performance wavelength converting crystal, having a chemical composition expressed as CsLiB6O10, and substituted cesium-lithium-borate crystals expressed by the following formula: Cs.sub.1-xLi.sub.1-yM.sub.x+yB.sub.6O.sub.10 or Cs.sub.2(1-z)Li.sub.2L.sub.zB.sub.12O.sub.20 (where, M is an alkali metal element, and L is an alkali earth metal element); a method for manufacturing same by heating and melting; and an optical apparatus using such crystals.