Abstract: A photoradical polymerization initiator that is environmentally friendly and composed solely of carbon, hydrogen and oxygen atoms, generating no acid that may cause corrosion during a radical polymerization reaction, and having a high radical polymerization initiation capacity to light having a wavelength of 350 nm to 420 nm. A photoradical polymerizable composition including a radical polymerizable compound and a photoradical polymerization initiator, where the photoradical polymerization initiator is a 1,4-dihydroxy-2-naphthoic acid compound represented by formula (1): where R is a hydrogen atom, a C1-10 alkyl group or a C6-14 aryl group, and X is a hydrogen atom, a C1-10 alkyl group, a C6-14 aryl group, a hydroxy group, a C1-10 alkoxy group or a C6-14 aryloxy group.