A calendar mechanism of a timepiece includes a month cam having a cam surface distinguishing between a long month (31 days) and a short month (30 days or less) and makes one rotation a year. A date indicator driving wheel has a date finger that makes one rotation every 24 hours and engages with a date wheel of a date indicator to rotate the date indicator. An operating lever structure has a proximal portion friction-engaged with an offset shaft to rotate around the offset shaft offset with respect to the rotation center of the date indicator driving wheel. The operating lever structure has a first distal end portion engaged with the month cam and a second distal end portion engaged with a month end tooth of the date indicator to effect additional date feeding by one day with respect to the date indicator at the end of a short month.