A 1,5-naphthyridine derivative represented by Formula [1] (in which R1, R2, R3, R4 and R5 represent a hydrogen atom, -L-Z (in which Z represents a non-aromatic heterocyclic group or the like; and L represents a single bond or the like), or the like, R6 represents -L-Z or the like, R7 and R8 represent a hydrogen atom or the like, and Q represents an oxygen atom or the like), or a salt thereof has an excellent inhibitory activity with respect to the PI3K-AKT pathway and the Ras-Raf-MEK-ERK pathway, and is useful for treatments such as prophylactic treatments and therapeutic treatments of diseases in which the PI3K-AKT pathway and the Ras-Raf-MEK-ERK pathway are involved.