近年來，主職之外的兼職與額外工作安排逐漸受到關注。第二工作反映勞工對勞動供給與工作配置的調整，其形成除與補充所得需求有關外，也可能受到地方景氣與主職工作條件影響。本文以臺灣全時受僱勞工為研究對象，使用2010至2022年「家庭動態調查」資料，串接縣市失業率等景氣指標，並將低度就業區分為收入型與技能型，採隨機效果Probit模型檢驗其對第二工作參與的影響。 實證結果顯示，失業率上升會顯著降低第二工作參與機率，說明第二工作較接近順景氣循環；但改以地方就業成長率衡量時則未呈一致。低度就業方面，收入型低度就業與第二工作參與呈顯著正向關聯，且此效果在不同群體間有所差異，例如在已婚男性與非六都樣本中較為明確；相較之下，技能型低度就業在整體樣本與多數分群皆未呈現顯著影響，僅在碩博學歷且對工作較不滿意者呈正向結果。故第二工作不宜直接視為勞動市場惡化或經濟弱勢的指標，而應結合地方景氣、主職條件及群體差異判斷。對於因主職收入不足而從事第二工作的勞工，政策應改善主職條件與職涯發展，例如提供職能培訓、職涯諮詢及就業媒合；對於地方工作機會有限，如非六都地區，可強化就業服務，並提供具勞動保障的兼職職缺資訊。;In recent years， second jobs and other forms of additional employment have received increasing attention. Holding a second job reflects how workers adjust their labor supply and work arrangements. Such decisions may be related not only to the need to supplement income but also to local economic conditions and primary-job characteristics. This study focuses on full-time employees in Taiwan and uses data from the Panel Study of Family Dynamics from 2010 to 2022. The individual-level data are linked with local economic indicators， including local unemployment rates. The analysis distinguishes between income-based and skill-based underemployment and employs a random-effects probit model to examine how local economic conditions and underemployment affect second-job participation.
The empirical results show that a higher local unemployment rate significantly reduces the probability of holding a second job， suggesting that second-job participation tends to be procyclical. However， the results are not consistent when local employment growth is used instead. Regarding underemployment， income-based underemployment is significantly and positively associated with second-job participation， with the relationship particularly evident among married men and workers residing outside Taiwan’s six special municipalities. By contrast， skill-based underemployment is not significantly associated with second-job participation in the overall sample or in most subgroup analyses. A positive relationship appears only among workers with master’s or doctoral degrees who report low job satisfaction. These findings suggest that holding a second job should not be viewed simply as an indicator of labor market deterioration or economic disadvantage. Instead， it should be considered alongside local economic conditions， primary-job characteristics， and differences across worker groups. For workers who take on a second job to make up for insufficient income from their primary job， policy measures should focus on improving primary-job conditions and career development opportunities， such as providing skills training， career counseling， and job-matching services. Where job opportunities are limited， such as the non-special municipalities， employment services should be strengthened， and information on part-time jobs that provide basic labor protections should be made more accessible.
