A novel therapeutic drug for malignant tumors, cancer stem cells, or fibrosis is obtained. A therapeutic drug for malignant tumors or cancer stem cells is used that includes at least one compound selected from the group consisting of compounds represented by formulas (1), (2), and (5), a salt thereof, or a solvate thereof. Alternatively, a therapeutic drug for fibrosis can be used that includes at least one compound selected from the group consisting of compounds represented by formulas (1), (2), and (5), a salt thereof, or a solvate thereof.