A diligent person; someone who works or studies hard.
彼は本当に勤勉家で、休日も勉強を欠かさない。
He is truly a diligent person and never misses studying even on his days off.
勤勉家の友人は、コツコツと準備を進めて合格した。
My diligent friend prepared steadily and passed the exam.
職場では勤勉家が評価されることが多い。
Hard workers are often valued in the workplace.