Jig, method for assembling robot using jig, and robot

A jig (1) is provided with: a first gear part (3) that can engage with an input gear (30) disposed inside a housing (10) by being inserted into the housing (10) from the outside of the housing (10); a torque applying unit (2) that is fixed to the first gear unit (3), is disposed outside the housing (10) in a state in which the first gear unit (10) is engaged with the input gear (30), and is capable of applying a torque to the first gear unit (3) about a first axis (L), which is the axis of the first gear unit (3); and a phase display unit (5) that is provided to the torque application unit (2) and displays the phase of the first gear unit (3) around the first axis (L). 一种夹具(1)，具备：第一齿轮部(3)，其能够通过从壳体(10)的外部插入壳体(10)的内部而与配置于壳体(10)的内部的输入齿轮(30)啮合；转矩施加部(2)，其固定于第一齿轮部(3)，并且在第一齿轮部(10)与输入齿轮(30)啮合的状态下配置于壳体(10)的外部，而且能够对第一齿轮部(3)施加围绕作为第一齿轮部(3)的轴线的第一轴线(L)的转矩；以及相位显示部(5)，其设置于转矩施加部(2)，并显示第一齿轮部(3)围绕第一轴线(L)的相位。