An object of the present invention is to provide novel apoptosis inhibitors and therapeutic agents for inner ear hearing impairment. As a pharmaceutical agent for this purpose, biguanide compounds represented by the following structural formula (I) or a rapamycin derivative represented by the following structural formula (II) as an active ingredient is provided: wherein R1 to R7 are each independently selected from a hydrogen atom, a halogen atom, or a C1-6 alkyl group, a C3-8 cycloalkyl group, a C6-10 aryl group, a 5- or 6-membered heteroaryl group, or a 5- or 6-membered non-aromatic heterocyclic group, each of which may have a substituent selected from a halogen atom, a cyano group, a C1-6 alkyl group, a C1-6 alkoxy group, a C1-6 alkoxy carbonyl group, a C3-8 cycloalkyl group, a C2-6 alkenyl group, a C2-6 alkynyl group, and a phenyl group; wherein R1 is a C1-6 alkyl or a C3-6 alkynyl, R2 is H, —CH2-OH or —CH2—CH2—OH, and X is ═O, (H, H) or (H, OH).