NOVELTY - A methylol compound (I) is new.    USE - In a charge transport layer useful in an electrophotographic photoreceptor (claimed), and in organic semiconductor devices such as organic electroluminescent devices, organic thin film transistors, and organic solar cells.    ADVANTAGE - The methylol compounds (I) have good charge transportability and are capable of forming highly-crosslinked layer having good resistance to mechanical strength and heat. Therefore, the methylol compound can be preferably used for various organic semiconductor devices such as electrophotographic photoreceptors. Since methylol compounds (I) have a main skeleton such that two triphenyl amine groups are connected with each other with a group between them in a molecule, the compounds have a charge transport function and low crystallinity while having good compatibility with other monomers and polymers such as polycarbonate. In addition, the methylol compounds can easily react with a hydroxyl group of an isocyanate compound, thus forming a crosslinked film having a high crosslinking degree while having a good charge transport property. Therefore, the methylol compounds can be preferably used as organic functional materials for use in preparing various organic semiconductor devices such as organic electrophotographic photoreceptors, organic electroluminescent devices, organic thin film transistors, and organic solar cells.    DETAILED DESCRIPTION - A methylol compound of formula (I) is new.    X1=-O-, -CH2-, -CH=CH-, or -CH2CH2-.    INDEPENDENT CLAIMS are included for the following:    (1) method for preparing the methylol compound (I);    (2) a charge transport layer comprising the methylol compound (I) and a binder resin;    (3) an electrophotographic photoreceptor comprising: a substrate; an optional undercoat layer located on the substrate; a charge generation layer; and the charge transport layer, where the charge generation layer and the charge transport layer are overlaid on the substrate or the optional undercoat layer; and    (4) a new aldehyde compound of formula (II).