This is Kogobutsu (香合仏), a pocket-sized Buddha statue which you can carry around while you travel. You can also keep this in your home without the worry of space.
In Japan, it's thought that all people, based on their Chinese zodiac sign, have a guardian Buddha or Bodhisattva who provides lifetime-protection. The belief is that by worshiping such Buddha or Bodhisattva, you can lead a peaceful life; and because we think that good fortune will come by placing objects related to your Chinese zodiac around you, Japanese believe that the guardian Buddha or Bodhisattva will also act as a guardian of good fortune, while protecting you from disaster and strengthening the good parts of your character and holding back the bad parts.
子 (Rat / 鼠): 千手観音(Senju Kannon)
丑 (Ox / 牛) : 虚空蔵菩薩(Kokuzo Bosatsu)
寅 (Tiger / 虎): 虚空蔵菩薩(Kokuzo Bosatsu)
卯 (Rabbit / 兔): 文殊菩薩(Monju Bosatsu)
辰 (Dragon / 龍): 普賢菩薩(Fugen Bosatsu)
巳 (Snake / 蛇): 普賢菩薩(Fugen Bosatsu)
午 (Horse / 馬): 勢至菩薩(Seishi Bosatsu)
未 (Goat / 羊): 大日如来(Dainichi Nyorai)
申 (Monkey / 猴): 大日如来(Dainichi Nyorai)
酉 (Rooster / 雞): 不動明王(Fudo Myo-o)
戌 (Dog / 狗): 阿弥陀如来(Amida Nyorai) (Amitabha)
亥 (Pig / 豬: 阿弥陀如来(Amida Nyorai) (Amitabha)