The present invention provides a crystal of (6S,9aS)-N-benzyl-8-({6-[3-(4-ethylpiperazin-1-yl)azetidin-1-yl]pyridin-2-yl} methyl)-6-(2-fluoro-4-hydroxybenzyl)-4,7-dioxo-2-(prop-2-en-1-yl)hexahydr o-2H-pyrazino[2,1-c][1,2,4]triazine-1(6H)-carboxamide.