As artificial intelligence (AI) receives wider attention in education, examining teachers' acceptance of AI (TAAI) becomes essential. However, existing instruments measuring TAAI reported limited validity evidence and faced some design challenges, such as missing informed definitions of AI to participants. To fill this gap, this study developed and validated a TAAI instrument. Based on the literature, we first identified five dimensions of TAAI, including perceived usefulness, perceived ease of use, behavioral intention, self-efficacy, and anxiety. Then we developed items to assess each dimension. We examined the face and content validity using expert review and think-aloud with pre-service teachers. Using the revised instrument, we collected responses from 274 pre-service teachers and examined the item discriminations to identify outlier items. We employed the confirmatory factor analysis and Cronbach's alpha to examine the construct validity, convergent validity, discriminant validity, and reliability. Results confirmed the dimensionality of the scale, resulting in 27 items distributed in five dimensions. The study exhibits robust validity and reliability evidence for TAAI, thus affirming its usefulness as a valid measurement instrument.