Provided are: a novel compound having an excellent Aurora-A-selective inhibitory activity and useful as an anti-cancer agent that can be administered orally a novel anti-tumor effect enhancer for a microtube agonist comprising a taxane-type anti-cancer agent and a combination therapy. A piperidine compound represented by general formula (I) (wherein R1 represents a carboxyl group, -C(=O)NR5R6, or an oxadiazolyl group which may have a C1-C6 alkyl group or a trifluoromethyl group as a substituent R2 represents a halogen atom, or a C1-C6 alkoxy group R3 represents a phenyl group which may have 1 to 3 groups independently selected from a halogen atom, a C1-C6 alkyl group, a C1-C6 alkoxy group and a trifluoromethyl group as a substituent or substituents R4 represents a hydrogen atom, or a C1-C6 alkyl group and R5 and R6 may be the same as or different from each other and independently represent a hydrogen atom, a C1-C6 alkyl group, or a C3-C6 cycloalkyl group, or R5, R6 and a nitrogen atom to which R5 and R6 are bound may together form a 3- to 6-membered nitrogenated saturated heterocyclic group) or a salt thereof.Se proporciona un compuesto novedoso que tiene excelente acción inhibidora selectiva de aurora A y es útil como agente anticanceroso oralmente administrable también, se proporciona un agente novedoso para la potenciación del efecto anti-tumor de agonistas de microtúbulos, que incluyen un agente anticanceroso de taxano, y una terapia combinación un compuesto de piperidina representado por una fórmula general (I) o una sal del mismo: en donde, R1 representa un grupo carboxilo, -C(=O)NR5R6 o un grupo oxodiazolilo que tiene opcionalmente un grupo alquilo C1-C6 o un grupo trifluorometilo como sustituyente R2 representa un átomo de halógeno o un grupo alcoxi C1-C6 R3 representa un grupo fenilo que tiene opcionalmente de 1 a 3 grupo(s) igual(es) o diferente (s) seleccionado (s) de un átomo de halógeno, un grupo alquilo C1-C6, un grupo alcoxi C1-C6 y un grupo trifluoro
