The crack energy density ε
J-integral which is the path independent expression of εare applied to creep problem and it is shown that εand its differential coefficient with respect to time ε
st are valid parameters to creep crack without any restriction on constitutive equation. The contents are as follows; (1) εand ε
st are introduced as creep crack parameters and it is shown that ε
st can be evaluated by path independent integral ε
Jst obtained by differentiating ε
J with respect to time. (2) It is pointed out that J'-integral (C
*-parameter) can be evaluated by newly-introduced ε'
Jst which is a path independent integral even to non-steady state creep, and the physical meaning of J' is clarified based on ε'
Jst. Also the relation between ε
st and J' is discussed ant the role of J' is made clear. (3) The validities of εand ε
st as creep crack parameters are numerically verified through finite element analyses.
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