The scintillator single crystal of the invention comprises a cerium-activated orthosilicate compound represented by the following general formula (1). The scintillator single crystal of the invention exhibits improved scintillation properties by reduced segregation between elements in the crystal ingot. Lm2−(x+y+z)LnxLuyCezSiO5  (1) (Wherein Lm represents at least one element selected from among Sc and Y and lanthanoid elements with lower atomic numbers than Lu, Ln represents at least one element selected from among Sc, Y, B, Al, Ga and In and lanthanoid elements with ion radii intermediate between Lm and Lu, x represents a value of greater than zero and no greater than 0.5, y represents a value of greater than 1 and less than 2, and z represents a value of greater than zero and no greater than 0.1.).