A front door 20 includes a first door component 22 and a second door component 34. The first door component 22 forms an inner side portion of a door main body 21, and the second door component forms an inner side portion of the door main body 21 and has functional parts located inside the vehicle. The first and second door components 22, 34 have
honeycomb structural bodies 23, 41, respectively. The
honeycomb structural bodies 23, 41 are entirely formed of
synthetic resin. The
honeycomb structural bodies 23, 41 include honeycomb portions 24, 42, which are composed of numerous tubular cells 26, 44, 45 separated by partition walls 25, 43, and sealing plate portions 27, 28, 46, 47 that are located on the outer side and the inner side of the honeycomb portions 24, 42 and seal the cells 26, 44. The door components 22, 34 are joined to each other at least at a part of the adjacent sealing plate portions 28, 46 of the honeycomb structural bodies 23, 41.